diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,3 +1,73 @@
+# 0.6.2.0
+
+## Added features
+
+* Added instances for `BeamSqlBackendIsString Postgres (CI String)` and
+  `BeamSqlBackendIsString Postgres (CI Text)`, allowing the use of `toTsVector`
+  over colums of type `citext` (#818)
+* Exposed the functionality to implement user-defined extensions via
+  `Database.Beam.Postgres.Extensions` (#819)
+
+## Bug fixes
+
+* Fixed an issue where using `pgSelectWith` with no common-table expressions
+  would lead to an invalid SQL query at runtime.
+
+# 0.6.1.0
+
+## Added features
+
+* Added file-mode `COPY ... TO 'file'` / `COPY ... FROM 'file'` support
+  via the new `MonadBeamCopyTo` / `MonadBeamCopyFrom` instances on `Pg`.
+  Smart constructors `copyToText` / `copyToCSV` (and `copyFromText` /
+  `copyFromCSV`, plus `*With` variants) build the per-format options
+  records. Note that this requires the `pg_write_server_files` /
+  `pg_read_server_files` role (or superuser) on the connecting role —
+  see `Database.Beam.Postgres.Extensions.Copy.File`.
+* Added streaming `COPY ... TO STDOUT` / `COPY ... FROM STDIN` support
+  via the new `MonadBeamCopyToStream` / `MonadBeamCopyFromStream`
+  instances on `Pg`. Smart constructors `copyToTextStream` /
+  `copyToCSVStream` / `copyFromTextStream` / `copyFromCSVStream` build
+  the per-format options. Streaming COPY does not require any special
+  role attribute and is the appropriate choice when the client and
+  server are on different hosts — see
+  `Database.Beam.Postgres.Extensions.Copy.Stream`.
+
+## Bug fixes
+
+* Fixed an issue where a window function applied over the result of `nub_` (or
+  the Postgres-specific `pgNubBy_`) would emit `DISTINCT` and the window
+  expression in the same `SELECT`, causing the window to evaluate against the
+  pre-deduplicated rows. The inner select is now materialised as a subquery
+  whenever it carries `DISTINCT`, `GROUP BY`, or `HAVING` (#756).
+
+# 0.6.0.0
+
+## Interface changes
+
+* Removed `week_` from `Database.Beam.Postgres.PgSpecific`. The same
+  functionality is now available in `beam-core` as a backend-agnostic
+  `week_` extract field; import it from `Database.Beam.Query.Extract` (or
+  re-exported through `Database.Beam`) instead.
+* Replaced the single `BeamSqlBackendHasSerial Postgres` instance with three
+  width-specific instances `BeamSqlBackendHasSerial Int16/Int32/Int64
+  Postgres`, mapping respectively to `smallserial`, `serial`, and
+  `bigserial`. Existing code using `genericSerial` for a `SqlSerial Int32`
+  column continues to work; other widths are now also supported (#534).
+
+## Added features
+
+* Implemented the new `runInsertReturningListWith` /
+  `runUpdateReturningListWith` / `runDeleteReturningListWith` class methods
+  on the `Pg` monad. These let callers project a subset of columns from the
+  affected rows of an `INSERT` / `UPDATE` / `DELETE ... RETURNING` (#801).
+* Implemented `weekField` for `PgExtractFieldSyntax`, supporting the new
+  backend-agnostic `week_` extract field from `beam-core`.
+
+## Updated dependencies
+
+* Bumped the lower bound on `beam-core` to `0.11`.
+
 # 0.5.6.1
 
 ## Bug fixes
diff --git a/Database/Beam/Postgres.hs b/Database/Beam/Postgres.hs
--- a/Database/Beam/Postgres.hs
+++ b/Database/Beam/Postgres.hs
@@ -16,74 +16,202 @@
 --
 -- For examples on how to use @beam-postgres@ usage, see
 -- <https://haskell-beam.github.io/beam/user-guide/backends/beam-postgres/ its manual>.
-
 module Database.Beam.Postgres
-  (  -- * Beam Postgres backend
-    Postgres(..), Pg, liftIOWithHandle
+  ( -- * Beam Postgres backend
+    Postgres (..),
+    Pg,
+    liftIOWithHandle,
 
     -- ** Executing actions against the backend
-  , runBeamPostgres, runBeamPostgresDebug
+    runBeamPostgres,
+    runBeamPostgresDebug,
 
     -- ** Postgres syntax
-  , PgCommandSyntax, PgSyntax
-  , PgSelectSyntax, PgInsertSyntax
-  , PgUpdateSyntax, PgDeleteSyntax
+    PgCommandSyntax,
+    PgSyntax,
+    PgSelectSyntax,
+    PgInsertSyntax,
+    PgUpdateSyntax,
+    PgDeleteSyntax,
 
-    -- * Beam URI support
-  , postgresUriSyntax
+    -- ** COPY support
 
-    -- * Postgres-specific features
-    -- ** Postgres-specific data types
+    --
+    -- File-mode @COPY@ support for Postgres. Use 'copyToText' / 'copyToCSV' (or 'copyFromText' /
+    -- 'copyFromCSV') for default options, and the @*With@ variants to override
+    -- format-specific fields.
 
-  , json, jsonb, uuid, money
-  , tsquery, tsvector, text, bytea
-  , unboundedArray
+    -- *** text format
+    copyToText,
+    copyToTextWith,
+    PgTextCopyToOptions (..),
+    defaultPgTextCopyToOptions,
+    copyFromText,
+    copyFromTextWith,
+    PgTextCopyFromOptions (..),
+    defaultPgTextCopyFromOptions,
 
-    -- *** @SERIAL@ support
-  , smallserial, serial, bigserial
+    -- *** CSV format
+    copyToCSV,
+    copyToCSVWith,
+    PgCSVCopyToOptions (..),
+    defaultPgCSVCopyToOptions,
+    copyFromCSV,
+    copyFromCSVWith,
+    PgCSVCopyFromOptions (..),
+    defaultPgCSVCopyFromOptions,
 
-  , module Database.Beam.Postgres.PgSpecific
-  , module Database.Beam.Postgres.TempTable
+    -- *** Top-level options sums
+    PgCopyToOptions,
+    PgCopyFromOptions,
 
-    -- ** Postgres extension support
-  , PgExtensionEntity, IsPgExtension(..)
-  , pgCreateExtension, pgDropExtension
-  , getPgExtension
+    -- ** Streaming COPY support
 
-    -- ** Utilities for defining custom instances
-  , fromPgIntegral
-  , fromPgScientificOrIntegral
+    --
+    -- Streaming @COPY ... TO STDOUT@ / @COPY ... FROM STDIN@.
+    -- Use 'copyToTextStream' / 'copyToCSVStream' (or 'copyFromTextStream' /
+    -- 'copyFromCSVStream') with the 'runCopyToStream' / 'runCopyFromStream'
+    -- runners from "Database.Beam.Backend.SQL.BeamExtensions".
 
-    -- ** Debug support
+    -- *** text format
+    copyToTextStream,
+    copyToTextStreamWith,
+    copyFromTextStream,
+    copyFromTextStreamWith,
 
-  , PgDebugStmt
-  , pgTraceStmtIO, pgTraceStmtIO'
-  , pgTraceStmt
+    -- *** CSV format
+    copyToCSVStream,
+    copyToCSVStreamWith,
+    copyFromCSVStream,
+    copyFromCSVStreamWith,
 
-  -- * @postgresql-simple@ re-exports
+    -- *** Top-level options sums
+    PgCopyToStreamOptions,
+    PgCopyFromStreamOptions,
 
-  , Pg.ResultError(..), Pg.SqlError(..)
+    -- * Beam URI support
+    postgresUriSyntax,
 
-  , Pg.Connection, Pg.ConnectInfo(..)
-  , Pg.defaultConnectInfo
+    -- * Postgres-specific features
 
-  , Pg.connectPostgreSQL, Pg.connect
-  , Pg.close
+    -- ** Postgres-specific data types
+    json,
+    jsonb,
+    uuid,
+    money,
+    tsquery,
+    tsvector,
+    text,
+    bytea,
+    unboundedArray,
 
-  ) where
+    -- *** @SERIAL@ support
+    smallserial,
+    serial,
+    bigserial,
+    module Database.Beam.Postgres.PgSpecific,
+    module Database.Beam.Postgres.TempTable,
 
+    -- ** Postgres extension support
+    PgExtensionEntity,
+    IsPgExtension (..),
+    pgCreateExtension,
+    pgDropExtension,
+    getPgExtension,
+
+    -- ** Utilities for defining custom instances
+    fromPgIntegral,
+    fromPgScientificOrIntegral,
+
+    -- ** Debug support
+    PgDebugStmt,
+    pgTraceStmtIO,
+    pgTraceStmtIO',
+    pgTraceStmt,
+
+    -- * @postgresql-simple@ re-exports
+    Pg.ResultError (..),
+    Pg.SqlError (..),
+    Pg.Connection,
+    Pg.ConnectInfo (..),
+    Pg.defaultConnectInfo,
+    Pg.connectPostgreSQL,
+    Pg.connect,
+    Pg.close,
+  )
+where
+
 import Database.Beam.Postgres.Connection
-import Database.Beam.Postgres.Full () -- for BeamHasInsertOnConflict instance
-import Database.Beam.Postgres.Syntax
-import Database.Beam.Postgres.Types
-import Database.Beam.Postgres.PgSpecific
-import Database.Beam.Postgres.Migrate ( tsquery, tsvector, text, bytea, unboundedArray
-                                      , json, jsonb, uuid, money, smallserial, serial
-                                      , bigserial)
-import Database.Beam.Postgres.Extensions ( PgExtensionEntity, IsPgExtension(..)
-                                         , pgCreateExtension, pgDropExtension
-                                         , getPgExtension )
+-- for BeamHasInsertOnConflict instance
+
 import Database.Beam.Postgres.Debug
+import Database.Beam.Postgres.Extensions
+  ( IsPgExtension (..),
+    PgExtensionEntity,
+    getPgExtension,
+    pgCreateExtension,
+    pgDropExtension,
+  )
+import Database.Beam.Postgres.Extensions.Copy.File
+  ( PgCSVCopyFromOptions (..),
+    PgCSVCopyToOptions (..),
+    PgCopyFromOptions,
+    PgCopyToOptions,
+    PgTextCopyFromOptions (..),
+    PgTextCopyToOptions (..),
+    copyFromCSV,
+    copyFromCSVWith,
+    copyFromText,
+    copyFromTextWith,
+    copyToCSV,
+    copyToCSVWith,
+    copyToText,
+    copyToTextWith,
+    defaultPgCSVCopyFromOptions,
+    defaultPgCSVCopyToOptions,
+    defaultPgTextCopyFromOptions,
+    defaultPgTextCopyToOptions,
+  )
+import Database.Beam.Postgres.Extensions.Copy.Stream
+  ( PgCopyFromStreamOptions,
+    PgCopyToStreamOptions,
+    copyFromCSVStream,
+    copyFromCSVStreamWith,
+    copyFromTextStream,
+    copyFromTextStreamWith,
+    copyToCSVStream,
+    copyToCSVStreamWith,
+    copyToTextStream,
+    copyToTextStreamWith,
+  )
+import Database.Beam.Postgres.Full ()
+import Database.Beam.Postgres.Migrate
+  ( bigserial,
+    bytea,
+    json,
+    jsonb,
+    money,
+    serial,
+    smallserial,
+    text,
+    tsquery,
+    tsvector,
+    unboundedArray,
+    uuid,
+  )
+import Database.Beam.Postgres.PgSpecific
+import Database.Beam.Postgres.Syntax
+  ( PgCommandSyntax,
+    PgDeleteSyntax,
+    PgInsertSyntax,
+    PgSelectSyntax,
+    PgSyntax,
+    PgUpdateSyntax,
+  )
 import Database.Beam.Postgres.TempTable
-
+import Database.Beam.Postgres.Types
+  ( Postgres (..),
+    fromPgIntegral,
+    fromPgScientificOrIntegral,
+  )
 import qualified Database.PostgreSQL.Simple as Pg
diff --git a/Database/Beam/Postgres/Connection.hs b/Database/Beam/Postgres/Connection.hs
--- a/Database/Beam/Postgres/Connection.hs
+++ b/Database/Beam/Postgres/Connection.hs
@@ -9,7 +9,6 @@
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE OverloadedStrings #-}
-{-# LANGUAGE CPP #-}
 {-# LANGUAGE BangPatterns #-}
 
 module Database.Beam.Postgres.Connection
@@ -25,14 +24,15 @@
 
   , postgresUriSyntax ) where
 
-import           Control.Exception (SomeException(..), throwIO)
-import           Data.IORef (newIORef, readIORef, writeIORef)
-import           Data.Vector (Vector)
-import qualified Data.Vector as V
+import           Control.Exception (SomeException(..), throwIO, onException, catch)
+import           Control.Monad (void)
 import           Control.Monad.Base (MonadBase(..))
 import           Control.Monad.Free.Church
 import           Control.Monad.IO.Class
 import           Control.Monad.Trans.Control (MonadBaseControl(..))
+import           Data.IORef (newIORef, readIORef, writeIORef)
+import           Data.Vector (Vector)
+import qualified Data.Vector as V
 
 import           Database.Beam hiding (runDelete, runUpdate, runInsert, insert)
 import           Database.Beam.Backend.SQL.BeamExtensions
@@ -41,6 +41,10 @@
 import           Database.Beam.Backend.URI
 import           Database.Beam.Schema.Tables
 
+import           Database.Beam.Postgres.Extensions.Copy.File
+                   ( PgCopyFromSyntax(..), PgCopyToSyntax(..) )
+import           Database.Beam.Postgres.Extensions.Copy.Stream
+                   ( PgCopyFromStreamSyntax(..), PgCopyToStreamSyntax(..) )
 import           Database.Beam.Postgres.Syntax
 import           Database.Beam.Postgres.Full
 import           Database.Beam.Postgres.Types
@@ -48,6 +52,7 @@
 import qualified Database.PostgreSQL.LibPQ as Pg hiding
   (Connection, escapeStringConn, escapeIdentifier, escapeByteaConn, exec)
 import qualified Database.PostgreSQL.Simple as Pg
+import qualified Database.PostgreSQL.Simple.Copy as PgCopy
 import qualified Database.PostgreSQL.Simple.FromField as Pg
 import qualified Database.PostgreSQL.Simple.Internal as Pg
   ( Field(..), RowParser(..)
@@ -407,13 +412,56 @@
                   Just x -> collectM (acc . (x:))
           in collectM id
 
-instance MonadBeamInsertReturning Postgres Pg where
-    runInsertReturningList i = do
-        let insertReturningCmd' = i `returning`
-              changeBeamRep (\(Columnar' (QExpr s) :: Columnar' (QExpr Postgres PostgresInaccessible) ty) ->
-                Columnar' (QExpr s) :: Columnar' (QExpr Postgres ()) ty)
+instance MonadBeamCopyTo Postgres Pg where
+    runCopyTo SqlCopyToNoColumns = pure ()
+    runCopyTo (SqlCopyTo (PgCopyToSyntax syntax)) =
+        runNoReturn (PgCommandSyntax PgCommandTypeDataUpdate syntax)
 
-        -- Make savepoint
+instance MonadBeamCopyFrom Postgres Pg where
+    runCopyFrom SqlCopyFromNoColumns = pure ()
+    runCopyFrom (SqlCopyFrom (PgCopyFromSyntax syntax)) =
+        runNoReturn (PgCommandSyntax PgCommandTypeDataUpdate syntax)
+
+instance MonadBeamCopyToStream Postgres Pg where
+    -- | `runCopyToStream` is exception-safe; if the output stream
+    -- produces an exception, the stream will be drained before the exception
+    -- is re-thrown
+    runCopyToStream SqlCopyToStreamNoColumns _ = pure ()
+    runCopyToStream (SqlCopyToStream (PgCopyToStreamSyntax syntax)) sink =
+        liftIOWithHandle $ \conn -> do
+          query <- pgRenderSyntax conn syntax
+          PgCopy.copy_ conn (Pg.Query query)
+          let loop onRow = do
+                PgCopy.getCopyData conn >>= \case
+                  PgCopy.CopyOutRow chunk -> onRow chunk >> loop onRow
+                  PgCopy.CopyOutDone _    -> pure ()
+              -- Like 'loop', but doesn't use the sink at all. This is used
+              -- to drain elements in the COPY stream before re-throwing an exception
+              drain = loop (const (pure ()))
+          loop sink `catch` (\(e::SomeException) -> drain >> throwIO e)
+
+
+instance MonadBeamCopyFromStream Postgres Pg where
+    -- | `runCopyFromStream` is exception-safe; if the input stream
+    -- produces an exception, the connection will be reset to a safe state,
+    -- aborting the COPY operation.
+    runCopyFromStream SqlCopyFromStreamNoColumns _ = pure ()
+    runCopyFromStream (SqlCopyFromStream (PgCopyFromStreamSyntax syntax)) producer =
+        liftIOWithHandle $ \conn -> do
+          query <- pgRenderSyntax conn syntax
+          let loop = 
+                producer >>= \case
+                  Just chunk -> PgCopy.putCopyData conn chunk >> loop
+                  Nothing    -> void $ PgCopy.putCopyEnd conn
+          PgCopy.copy_ conn (Pg.Query query)
+          loop `onException` PgCopy.putCopyError conn mempty
+
+instance MonadBeamInsertReturning Postgres Pg where
+    runInsertReturningListWith i mkProjection = do
+        let pgProj tbl = mkProjection (changeBeamRep
+              (\(Columnar' (QExpr s) :: Columnar' (QExpr Postgres PostgresInaccessible) ty) ->
+                Columnar' (QExpr s) :: Columnar' (QExpr Postgres ()) ty) tbl)
+            insertReturningCmd' = i `returning` pgProj
         case insertReturningCmd' of
           PgInsertReturningEmpty ->
             pure []
@@ -421,11 +469,11 @@
             runReturningList (PgCommandSyntax PgCommandTypeDataUpdateReturning insertReturningCmd)
 
 instance MonadBeamUpdateReturning Postgres Pg where
-    runUpdateReturningList u = do
-        let updateReturningCmd' = u `returning`
-              changeBeamRep (\(Columnar' (QExpr s) :: Columnar' (QExpr Postgres PostgresInaccessible) ty) ->
-                Columnar' (QExpr s) :: Columnar' (QExpr Postgres ()) ty)
-
+    runUpdateReturningListWith u mkProjection = do
+        let pgProj tbl = mkProjection (changeBeamRep
+              (\(Columnar' (QExpr s) :: Columnar' (QExpr Postgres PostgresInaccessible) ty) ->
+                Columnar' (QExpr s) :: Columnar' (QExpr Postgres ()) ty) tbl)
+            updateReturningCmd' = u `returning` pgProj
         case updateReturningCmd' of
           PgUpdateReturningEmpty ->
             pure []
@@ -433,9 +481,9 @@
             runReturningList (PgCommandSyntax PgCommandTypeDataUpdateReturning updateReturningCmd)
 
 instance MonadBeamDeleteReturning Postgres Pg where
-    runDeleteReturningList d = do
-        let PgDeleteReturning deleteReturningCmd = d `returning`
-              changeBeamRep (\(Columnar' (QExpr s) :: Columnar' (QExpr Postgres PostgresInaccessible) ty) ->
-                Columnar' (QExpr s) :: Columnar' (QExpr Postgres ()) ty)
-
+    runDeleteReturningListWith d mkProjection = do
+        let pgProj tbl = mkProjection (changeBeamRep
+              (\(Columnar' (QExpr s) :: Columnar' (QExpr Postgres PostgresInaccessible) ty) ->
+                Columnar' (QExpr s) :: Columnar' (QExpr Postgres ()) ty) tbl)
+            PgDeleteReturning deleteReturningCmd = d `returning` pgProj
         runReturningList (PgCommandSyntax PgCommandTypeDataUpdateReturning deleteReturningCmd)
diff --git a/Database/Beam/Postgres/Extensions.hs b/Database/Beam/Postgres/Extensions.hs
--- a/Database/Beam/Postgres/Extensions.hs
+++ b/Database/Beam/Postgres/Extensions.hs
@@ -1,6 +1,5 @@
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
 {-# LANGUAGE UndecidableInstances #-}
-{-# LANGUAGE CPP #-}
 
 -- | Postgres extensions are run-time loadable plugins that can extend Postgres
 -- functionality. Extensions are part of the database schema.
@@ -10,9 +9,29 @@
 -- the extension in a particular backend. @beam-postgres@ provides predicates
 -- and checks for @beam-migrate@ which allow extensions to be included as
 -- regular parts of beam migrations.
-module Database.Beam.Postgres.Extensions where
+module Database.Beam.Postgres.Extensions (
+  -- * Handling extensions
+  PgExtensionEntity,
+  getPgExtension,
 
+  -- * Defining extensions
+  IsPgExtension(..),
+  -- ** Helpers
+  PgExpr,
+  LiftPg,
+  funcE,
+
+  -- * Migrations
+  PgHasExtension(..),
+  pgCreateExtension,
+  pgDropExtension,
+  pgExtensionActionProvider,
+) where
+
 import           Database.Beam
+import           Database.Beam.Backend.SQL ( IsSql92ExpressionSyntax(..), IsSql92FieldNameSyntax(..),
+                                             IsSql99ExpressionSyntax, IsSql99FunctionExpressionSyntax(..)
+                                           )
 import           Database.Beam.Schema.Tables
 
 import           Database.Beam.Postgres.Types
@@ -122,6 +141,21 @@
                -> extension
 getPgExtension (DatabaseEntity (PgDatabaseExtension _ ext)) = ext
 
+-- *** Helpers to write postgres user-defined extensions
+
+-- | @since 0.6.2.0
+type PgExpr ctxt s = QGenExpr ctxt Postgres s
+
+-- | @since 0.6.2.0
+type family LiftPg ctxt s fn where
+  LiftPg ctxt s (Maybe a -> b) = Maybe (PgExpr ctxt s a) -> LiftPg ctxt s b
+  LiftPg ctxt s (a -> b) = PgExpr ctxt s a -> LiftPg ctxt s b
+  LiftPg ctxt s a = PgExpr ctxt s a
+
+-- | @since 0.6.2.0
+funcE :: IsSql99ExpressionSyntax expr => Text -> [expr] -> expr
+funcE nm = functionCallE (fieldE (unqualifiedField nm))
+
 -- *** Migrations support for extensions
 
 -- | 'Migration' representing the Postgres @CREATE EXTENSION@ command. Because
@@ -192,3 +226,4 @@
      pure (PotentialAction (HS.fromList [p extP]) mempty
                            (pure (MigrationCommand cmd MigrationKeepsData))
                            ("Unload the postgres extension " <> ext) 1)
+
diff --git a/Database/Beam/Postgres/Extensions/Copy/File.hs b/Database/Beam/Postgres/Extensions/Copy/File.hs
new file mode 100644
--- /dev/null
+++ b/Database/Beam/Postgres/Extensions/Copy/File.hs
@@ -0,0 +1,421 @@
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE TypeFamilies #-}
+
+module Database.Beam.Postgres.Extensions.Copy.File
+  ( PgCopyToSyntax (..),
+    PgCopyToSourceSyntax (..),
+    PgCopyFromSyntax (..),
+    PgCopyFromSourceSyntax (..),
+
+    -- * COPY options
+    PgCopyToOptions,
+    PgCopyFromOptions,
+
+    -- ** text
+    copyToText,
+    copyToTextWith,
+    PgTextCopyToOptions (..),
+    defaultPgTextCopyToOptions,
+    copyFromText,
+    copyFromTextWith,
+    PgTextCopyFromOptions (..),
+    defaultPgTextCopyFromOptions,
+
+    -- ** CSV
+    copyToCSV,
+    copyToCSVWith,
+    PgCSVCopyToOptions (..),
+    defaultPgCSVCopyToOptions,
+    copyFromCSV,
+    copyFromCSVWith,
+    PgCSVCopyFromOptions (..),
+    defaultPgCSVCopyFromOptions,
+
+    -- * Internal — exposed for use by sibling modules
+    emitOptionList,
+    textCopyToFields,
+    csvCopyToFields,
+    textCopyFromFields,
+    csvCopyFromFields,
+  )
+where
+
+import qualified Data.List.NonEmpty as NE
+import Data.Maybe (catMaybes)
+import Data.Text (Text)
+import qualified Data.Text as T
+import Database.Beam.Backend.SQL.BeamExtensions
+  ( IsSqlCopyFromSourceSyntax (..),
+    IsSqlCopyFromSyntax (..),
+    IsSqlCopyToSourceSyntax (..),
+    IsSqlCopyToSyntax (..),
+  )
+import Database.Beam.Postgres.Syntax
+  ( PgSelectSyntax (..),
+    PgSyntax,
+    emit,
+    pgBoolLit,
+    pgCharLit,
+    pgParens,
+    pgQuotedIdentifier,
+    pgSepBy,
+    pgStringLit,
+  )
+
+-- | PostgreSQL @COPY ... TO@ source syntax. Wraps the table name (with
+-- optional column list) or a @SELECT@ subquery.
+--
+-- @since 0.6.1.0
+newtype PgCopyToSourceSyntax = PgCopyToSourceSyntax {fromPgCopyToSource :: PgSyntax}
+
+-- | PostgreSQL @COPY ... TO@ statement syntax.
+--
+-- @since 0.6.1.0
+newtype PgCopyToSyntax = PgCopyToSyntax {fromPgCopyTo :: PgSyntax}
+
+-- | PostgreSQL @COPY ... FROM@ source syntax. Just the table name plus
+-- optional column list — Postgres @COPY ... FROM@ does not accept a SELECT.
+--
+-- @since 0.6.1.0
+newtype PgCopyFromSourceSyntax = PgCopyFromSourceSyntax {fromPgCopyFromSource :: PgSyntax}
+
+-- | PostgreSQL @COPY ... FROM@ statement syntax.
+--
+-- @since 0.6.1.0
+newtype PgCopyFromSyntax = PgCopyFromSyntax {fromPgCopyFrom :: PgSyntax}
+
+instance IsSqlCopyToSourceSyntax PgCopyToSourceSyntax where
+  type SqlCopyToSourceSelectSyntax PgCopyToSourceSyntax = PgSelectSyntax
+
+  copyTableToSyntax mSchema tableName' mColumns =
+    PgCopyToSourceSyntax $
+      maybe mempty (\schema -> pgQuotedIdentifier schema <> emit ".") mSchema
+        <> pgQuotedIdentifier tableName'
+        <> case mColumns of
+          Nothing -> mempty
+          Just cols -> pgParens $ pgSepBy (emit ", ") (map pgQuotedIdentifier (NE.toList cols))
+
+  copySelectToSyntax (PgSelectSyntax select) = PgCopyToSourceSyntax $ pgParens select
+
+instance IsSqlCopyToSyntax PgCopyToSyntax where
+  type SqlCopyToSourceSyntax PgCopyToSyntax = PgCopyToSourceSyntax
+  type SqlCopyToParams PgCopyToSyntax = PgCopyToOptions
+
+  copyToStmt (PgCopyToSourceSyntax source) options =
+    let (filepath, optionsSyntax) = emitPgCopyToOptions options
+     in PgCopyToSyntax $
+          mconcat
+            [ emit "COPY ",
+              source,
+              emit " TO ",
+              pgStringLit (T.pack filepath),
+              optionsSyntax
+            ]
+
+instance IsSqlCopyFromSourceSyntax PgCopyFromSourceSyntax where
+  copyTableFromSyntax mSchema tableName' mColumns =
+    PgCopyFromSourceSyntax $
+      maybe mempty (\schema -> pgQuotedIdentifier schema <> emit ".") mSchema
+        <> pgQuotedIdentifier tableName'
+        <> case mColumns of
+          Nothing -> mempty
+          Just cols -> pgParens $ pgSepBy (emit ", ") (map pgQuotedIdentifier (NE.toList cols))
+
+instance IsSqlCopyFromSyntax PgCopyFromSyntax where
+  type SqlCopyFromSourceSyntax PgCopyFromSyntax = PgCopyFromSourceSyntax
+  type SqlCopyFromParams PgCopyFromSyntax = PgCopyFromOptions
+
+  copyFromStmt (PgCopyFromSourceSyntax source) options =
+    let (filepath, optionsSyntax) = emitPgCopyFromOptions options
+     in PgCopyFromSyntax $
+          mconcat
+            [ emit "COPY ",
+              source,
+              emit " FROM ",
+              pgStringLit (T.pack filepath),
+              optionsSyntax
+            ]
+
+-- | Options for PostgreSQL's @COPY ... TO@ statement, tagged by the output
+-- format. Use 'copyToText' or 'copyToCSV' to construct.
+--
+-- See <https://www.postgresql.org/docs/current/sql-copy.html the PostgreSQL COPY documentation>
+-- for the full set of options each format supports.
+--
+-- @since 0.6.1.0
+data PgCopyToOptions
+  = PgCopyToText !FilePath !PgTextCopyToOptions
+  | PgCopyToCSV !FilePath !PgCSVCopyToOptions
+  deriving (Eq, Show)
+
+-- | Copy to a text file at the given path with default options.
+-- Use 'copyToTextWith' to override.
+--
+-- @since 0.6.1.0
+copyToText :: FilePath -> PgCopyToOptions
+copyToText path = PgCopyToText path defaultPgTextCopyToOptions
+
+-- | Copy to a text file at the given path with the given options.
+--
+-- @since 0.6.1.0
+copyToTextWith :: FilePath -> PgTextCopyToOptions -> PgCopyToOptions
+copyToTextWith = PgCopyToText
+
+-- | Copy to a CSV file at the given path with default options.
+-- Use 'copyToCSVWith' to override.
+--
+-- @since 0.6.1.0
+copyToCSV :: FilePath -> PgCopyToOptions
+copyToCSV path = PgCopyToCSV path defaultPgCSVCopyToOptions
+
+-- | Copy to a CSV file at the given path with the given options.
+--
+-- @since 0.6.1.0
+copyToCSVWith :: FilePath -> PgCSVCopyToOptions -> PgCopyToOptions
+copyToCSVWith = PgCopyToCSV
+
+-- | Options for PostgreSQL's @COPY ... FROM@ statement, tagged by the input
+-- format. Use 'copyFromText' or 'copyFromCSV' to construct.
+--
+-- @since 0.6.1.0
+data PgCopyFromOptions
+  = PgCopyFromText !FilePath !PgTextCopyFromOptions
+  | PgCopyFromCSV !FilePath !PgCSVCopyFromOptions
+  deriving (Eq, Show)
+
+-- | Copy from a text file at the given path with default options.
+-- Use 'copyFromTextWith' to override.
+--
+-- @since 0.6.1.0
+copyFromText :: FilePath -> PgCopyFromOptions
+copyFromText path = PgCopyFromText path defaultPgTextCopyFromOptions
+
+-- | Copy from a text file at the given path with the given options.
+--
+-- @since 0.6.1.0
+copyFromTextWith :: FilePath -> PgTextCopyFromOptions -> PgCopyFromOptions
+copyFromTextWith = PgCopyFromText
+
+-- | Copy from a CSV file at the given path with default options.
+-- Use 'copyFromCSVWith' to override.
+--
+-- @since 0.6.1.0
+copyFromCSV :: FilePath -> PgCopyFromOptions
+copyFromCSV path = PgCopyFromCSV path defaultPgCSVCopyFromOptions
+
+-- | Copy from a CSV file at the given path with the given options.
+--
+-- @since 0.6.1.0
+copyFromCSVWith :: FilePath -> PgCSVCopyFromOptions -> PgCopyFromOptions
+copyFromCSVWith = PgCopyFromCSV
+
+-- | Options for the @text@ format on @COPY ... TO@.
+--
+-- @since 0.6.1.0
+data PgTextCopyToOptions = PgTextCopyToOptions
+  { -- | @DELIMITER@: single-character column delimiter. Defaults to TAB.
+    pgTextCopyToDelimiter :: Maybe Char,
+    -- | @NULL@: token written for SQL @NULL@ values. Defaults to @\\N@.
+    pgTextCopyToNullStr :: Maybe Text,
+    -- | @HEADER@: emit a header row with column names.
+    pgTextCopyToHeader :: Maybe Bool,
+    -- | @ENCODING@: client-encoding override for the file.
+    pgTextCopyToEncoding :: Maybe Text
+  }
+  deriving (Eq, Show)
+
+-- | All-'Nothing' 'PgTextCopyToOptions'; a sensible starting point for
+-- record-update overrides.
+--
+-- @since 0.6.1.0
+defaultPgTextCopyToOptions :: PgTextCopyToOptions
+defaultPgTextCopyToOptions =
+  PgTextCopyToOptions
+    { pgTextCopyToDelimiter = Nothing,
+      pgTextCopyToNullStr = Nothing,
+      pgTextCopyToHeader = Nothing,
+      pgTextCopyToEncoding = Nothing
+    }
+
+-- | Options for the @csv@ format on @COPY ... TO@.
+--
+-- @since 0.6.1.0
+data PgCSVCopyToOptions = PgCSVCopyToOptions
+  { -- | @DELIMITER@: single-character column delimiter. Defaults to a comma.
+    pgCsvCopyToDelimiter :: Maybe Char,
+    -- | @NULL@: token written for SQL @NULL@ values. Defaults to the empty
+    -- string.
+    pgCsvCopyToNullStr :: Maybe Text,
+    -- | @HEADER@: emit a header row with column names.
+    pgCsvCopyToHeader :: Maybe Bool,
+    -- | @QUOTE@: single-character quote character. Defaults to @\"@.
+    pgCsvCopyToQuote :: Maybe Char,
+    -- | @ESCAPE@: single-character escape character. Defaults to the
+    -- value of 'pgCsvCopyToQuote'.
+    pgCsvCopyToEscape :: Maybe Char,
+    -- | @ENCODING@: client-encoding override for the file.
+    pgCsvCopyToEncoding :: Maybe Text
+  }
+  deriving (Eq, Show)
+
+-- | All-'Nothing' 'PgCSVCopyToOptions'.
+--
+-- @since 0.6.1.0
+defaultPgCSVCopyToOptions :: PgCSVCopyToOptions
+defaultPgCSVCopyToOptions =
+  PgCSVCopyToOptions
+    { pgCsvCopyToDelimiter = Nothing,
+      pgCsvCopyToNullStr = Nothing,
+      pgCsvCopyToHeader = Nothing,
+      pgCsvCopyToQuote = Nothing,
+      pgCsvCopyToEscape = Nothing,
+      pgCsvCopyToEncoding = Nothing
+    }
+
+-- | Options for the @text@ format on @COPY ... FROM@.
+--
+-- @since 0.6.1.0
+data PgTextCopyFromOptions = PgTextCopyFromOptions
+  { -- | @DELIMITER@: single-character column delimiter. Defaults to TAB.
+    pgTextCopyFromDelimiter :: Maybe Char,
+    -- | @NULL@: token to interpret as SQL @NULL@. Defaults to @\\N@.
+    pgTextCopyFromNullStr :: Maybe Text,
+    -- | @HEADER@: skip the first line as a header row.
+    pgTextCopyFromHeader :: Maybe Bool,
+    -- | @ENCODING@: client-encoding override for the file.
+    pgTextCopyFromEncoding :: Maybe Text,
+    -- | @FREEZE@: skip WAL when loading; only legal under specific
+    -- conditions (see the PostgreSQL @COPY@ documentation).
+    pgTextCopyFromFreeze :: Maybe Bool
+  }
+  deriving (Eq, Show)
+
+-- | All-'Nothing' 'PgTextCopyFromOptions'.
+--
+-- @since 0.6.1.0
+defaultPgTextCopyFromOptions :: PgTextCopyFromOptions
+defaultPgTextCopyFromOptions =
+  PgTextCopyFromOptions
+    { pgTextCopyFromDelimiter = Nothing,
+      pgTextCopyFromNullStr = Nothing,
+      pgTextCopyFromHeader = Nothing,
+      pgTextCopyFromEncoding = Nothing,
+      pgTextCopyFromFreeze = Nothing
+    }
+
+-- | Options for the @csv@ format on @COPY ... FROM@.
+--
+-- @since 0.6.1.0
+data PgCSVCopyFromOptions = PgCSVCopyFromOptions
+  { -- | @DELIMITER@: single-character column delimiter. Defaults to a comma.
+    pgCsvCopyFromDelimiter :: Maybe Char,
+    -- | @NULL@: token to interpret as SQL @NULL@. Defaults to the empty
+    -- string.
+    pgCsvCopyFromNullStr :: Maybe Text,
+    -- | @HEADER@: skip the first line as a header row.
+    pgCsvCopyFromHeader :: Maybe Bool,
+    -- | @QUOTE@: single-character quote character. Defaults to @\"@.
+    pgCsvCopyFromQuote :: Maybe Char,
+    -- | @ESCAPE@: single-character escape character. Defaults to the
+    -- value of 'pgCsvCopyFromQuote'.
+    pgCsvCopyFromEscape :: Maybe Char,
+    -- | @ENCODING@: client-encoding override for the file.
+    pgCsvCopyFromEncoding :: Maybe Text,
+    -- | @FREEZE@: skip WAL when loading; only legal under specific
+    -- conditions (see the PostgreSQL @COPY@ documentation).
+    pgCsvCopyFromFreeze :: Maybe Bool
+  }
+  deriving (Eq, Show)
+
+-- | All-'Nothing' 'PgCSVCopyFromOptions'; a sensible starting point for
+-- record-update overrides.
+--
+-- @since 0.6.1.0
+defaultPgCSVCopyFromOptions :: PgCSVCopyFromOptions
+defaultPgCSVCopyFromOptions =
+  PgCSVCopyFromOptions
+    { pgCsvCopyFromDelimiter = Nothing,
+      pgCsvCopyFromNullStr = Nothing,
+      pgCsvCopyFromHeader = Nothing,
+      pgCsvCopyFromQuote = Nothing,
+      pgCsvCopyFromEscape = Nothing,
+      pgCsvCopyFromEncoding = Nothing,
+      pgCsvCopyFromFreeze = Nothing
+    }
+
+-- * Emission
+
+emitPgCopyToOptions :: PgCopyToOptions -> (FilePath, PgSyntax)
+emitPgCopyToOptions (PgCopyToText fp o) = (fp, emitOptionList (emit "text") (textCopyToFields o))
+emitPgCopyToOptions (PgCopyToCSV fp o) = (fp, emitOptionList (emit "csv") (csvCopyToFields o))
+
+emitPgCopyFromOptions :: PgCopyFromOptions -> (FilePath, PgSyntax)
+emitPgCopyFromOptions (PgCopyFromText fp o) = (fp, emitOptionList (emit "text") (textCopyFromFields o))
+emitPgCopyFromOptions (PgCopyFromCSV fp o) = (fp, emitOptionList (emit "csv") (csvCopyFromFields o))
+
+-- | Render @ (FORMAT FMT, OPT1 …, OPT2 …)@. The @FORMAT@ entry is always
+-- present since the constructor of the options value pins it.
+--
+-- @since 0.6.1.0
+emitOptionList :: PgSyntax -> [PgSyntax] -> PgSyntax
+emitOptionList fmt items =
+  emit " ("
+    <> pgSepBy (emit ", ") ((emit "FORMAT " <> fmt) : items)
+    <> emit ")"
+
+-- | Render the per-option items for a 'PgTextCopyToOptions' value.
+--
+-- @since 0.6.1.0
+textCopyToFields :: PgTextCopyToOptions -> [PgSyntax]
+textCopyToFields o =
+  catMaybes
+    [ fmap (\c -> emit "DELIMITER " <> pgCharLit c) (pgTextCopyToDelimiter o),
+      fmap (\s -> emit "NULL " <> pgStringLit s) (pgTextCopyToNullStr o),
+      fmap (\b -> emit "HEADER " <> pgBoolLit b) (pgTextCopyToHeader o),
+      fmap (\s -> emit "ENCODING " <> pgStringLit s) (pgTextCopyToEncoding o)
+    ]
+
+-- | Render the per-option items for a 'PgCSVCopyToOptions' value.
+--
+-- @since 0.6.1.0
+csvCopyToFields :: PgCSVCopyToOptions -> [PgSyntax]
+csvCopyToFields o =
+  catMaybes
+    [ fmap (\c -> emit "DELIMITER " <> pgCharLit c) (pgCsvCopyToDelimiter o),
+      fmap (\s -> emit "NULL " <> pgStringLit s) (pgCsvCopyToNullStr o),
+      fmap (\b -> emit "HEADER " <> pgBoolLit b) (pgCsvCopyToHeader o),
+      fmap (\c -> emit "QUOTE " <> pgCharLit c) (pgCsvCopyToQuote o),
+      fmap (\c -> emit "ESCAPE " <> pgCharLit c) (pgCsvCopyToEscape o),
+      fmap (\s -> emit "ENCODING " <> pgStringLit s) (pgCsvCopyToEncoding o)
+    ]
+
+-- | Render the per-option items for a 'PgTextCopyFromOptions' value.
+--
+-- @since 0.6.1.0
+textCopyFromFields :: PgTextCopyFromOptions -> [PgSyntax]
+textCopyFromFields o =
+  catMaybes
+    [ fmap (\c -> emit "DELIMITER " <> pgCharLit c) (pgTextCopyFromDelimiter o),
+      fmap (\s -> emit "NULL " <> pgStringLit s) (pgTextCopyFromNullStr o),
+      fmap (\b -> emit "HEADER " <> pgBoolLit b) (pgTextCopyFromHeader o),
+      fmap (\s -> emit "ENCODING " <> pgStringLit s) (pgTextCopyFromEncoding o),
+      fmap (\b -> emit "FREEZE " <> pgBoolLit b) (pgTextCopyFromFreeze o)
+    ]
+
+-- | Render the per-option items for a 'PgCSVCopyFromOptions' value.
+--
+-- @since 0.6.1.0
+csvCopyFromFields :: PgCSVCopyFromOptions -> [PgSyntax]
+csvCopyFromFields o =
+  catMaybes
+    [ fmap (\c -> emit "DELIMITER " <> pgCharLit c) (pgCsvCopyFromDelimiter o),
+      fmap (\s -> emit "NULL " <> pgStringLit s) (pgCsvCopyFromNullStr o),
+      fmap (\b -> emit "HEADER " <> pgBoolLit b) (pgCsvCopyFromHeader o),
+      fmap (\c -> emit "QUOTE " <> pgCharLit c) (pgCsvCopyFromQuote o),
+      fmap (\c -> emit "ESCAPE " <> pgCharLit c) (pgCsvCopyFromEscape o),
+      fmap (\s -> emit "ENCODING " <> pgStringLit s) (pgCsvCopyFromEncoding o),
+      fmap (\b -> emit "FREEZE " <> pgBoolLit b) (pgCsvCopyFromFreeze o)
+    ]
diff --git a/Database/Beam/Postgres/Extensions/Copy/Stream.hs b/Database/Beam/Postgres/Extensions/Copy/Stream.hs
new file mode 100644
--- /dev/null
+++ b/Database/Beam/Postgres/Extensions/Copy/Stream.hs
@@ -0,0 +1,175 @@
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE TypeFamilies #-}
+
+module Database.Beam.Postgres.Extensions.Copy.Stream
+  ( PgCopyToStreamSyntax (..),
+    PgCopyFromStreamSyntax (..),
+
+    -- * COPY options
+    PgCopyToStreamOptions,
+    PgCopyFromStreamOptions,
+
+    -- ** text
+    copyToTextStream,
+    copyToTextStreamWith,
+    copyFromTextStream,
+    copyFromTextStreamWith,
+
+    -- ** CSV
+    copyToCSVStream,
+    copyToCSVStreamWith,
+    copyFromCSVStream,
+    copyFromCSVStreamWith,
+  )
+where
+
+import Database.Beam.Backend.SQL.BeamExtensions
+  ( IsSqlCopyFromStreamSyntax (..),
+    IsSqlCopyToStreamSyntax (..),
+  )
+import Database.Beam.Postgres.Extensions.Copy.File
+  ( PgCSVCopyFromOptions (..),
+    PgCSVCopyToOptions (..),
+    PgCopyFromSourceSyntax (..),
+    PgCopyToSourceSyntax (..),
+    PgTextCopyFromOptions (..),
+    PgTextCopyToOptions (..),
+    csvCopyFromFields,
+    csvCopyToFields,
+    defaultPgCSVCopyFromOptions,
+    defaultPgCSVCopyToOptions,
+    defaultPgTextCopyFromOptions,
+    defaultPgTextCopyToOptions,
+    emitOptionList,
+    textCopyFromFields,
+    textCopyToFields,
+  )
+import Database.Beam.Postgres.Syntax (PgSyntax, emit)
+
+-- | PostgreSQL streaming @COPY ... TO STDOUT@ statement syntax.
+--
+-- @since 0.6.1.0
+newtype PgCopyToStreamSyntax = PgCopyToStreamSyntax {fromPgCopyToStream :: PgSyntax}
+
+-- | PostgreSQL streaming @COPY ... FROM STDIN@ statement syntax.
+--
+-- @since 0.6.1.0
+newtype PgCopyFromStreamSyntax = PgCopyFromStreamSyntax {fromPgCopyFromStream :: PgSyntax}
+
+instance IsSqlCopyToStreamSyntax PgCopyToStreamSyntax where
+  type SqlCopyToStreamSourceSyntax PgCopyToStreamSyntax = PgCopyToSourceSyntax
+  type SqlCopyToStreamParams PgCopyToStreamSyntax = PgCopyToStreamOptions
+
+  copyToStreamStmt (PgCopyToSourceSyntax source) options =
+    PgCopyToStreamSyntax $
+      mconcat
+        [ emit "COPY ",
+          source,
+          emit " TO STDOUT",
+          emitPgCopyToStreamOptions options
+        ]
+
+instance IsSqlCopyFromStreamSyntax PgCopyFromStreamSyntax where
+  type SqlCopyFromStreamSourceSyntax PgCopyFromStreamSyntax = PgCopyFromSourceSyntax
+  type SqlCopyFromStreamParams PgCopyFromStreamSyntax = PgCopyFromStreamOptions
+
+  copyFromStreamStmt (PgCopyFromSourceSyntax source) options =
+    PgCopyFromStreamSyntax $
+      mconcat
+        [ emit "COPY ",
+          source,
+          emit " FROM STDIN",
+          emitPgCopyFromStreamOptions options
+        ]
+
+-- | Options for PostgreSQL's streaming @COPY ... TO STDOUT@ statement,
+-- tagged by the output format.
+--
+-- See <https://www.postgresql.org/docs/current/sql-copy.html the PostgreSQL COPY documentation>
+-- for the full set of options each format supports.
+--
+-- @since 0.6.1.0
+data PgCopyToStreamOptions
+  = PgCopyToStreamText !PgTextCopyToOptions
+  | PgCopyToStreamCSV !PgCSVCopyToOptions
+  deriving (Eq, Show)
+
+-- | Stream out using the @text@ format with default options.
+-- Use 'copyToTextStreamWith' to override.
+--
+-- @since 0.6.1.0
+copyToTextStream :: PgCopyToStreamOptions
+copyToTextStream = PgCopyToStreamText defaultPgTextCopyToOptions
+
+-- | Stream out using the @text@ format with the given options.
+--
+-- @since 0.6.1.0
+copyToTextStreamWith :: PgTextCopyToOptions -> PgCopyToStreamOptions
+copyToTextStreamWith = PgCopyToStreamText
+
+-- | Stream out using the @csv@ format with default options.
+-- Use 'copyToCSVStreamWith' to override.
+--
+-- @since 0.6.1.0
+copyToCSVStream :: PgCopyToStreamOptions
+copyToCSVStream = PgCopyToStreamCSV defaultPgCSVCopyToOptions
+
+-- | Stream out using the @csv@ format with the given options.
+--
+-- @since 0.6.1.0
+copyToCSVStreamWith :: PgCSVCopyToOptions -> PgCopyToStreamOptions
+copyToCSVStreamWith = PgCopyToStreamCSV
+
+-- | Options for PostgreSQL's streaming @COPY ... FROM STDIN@ statement,
+-- tagged by the input format.
+--
+-- @since 0.6.1.0
+data PgCopyFromStreamOptions
+  = PgCopyFromStreamText !PgTextCopyFromOptions
+  | PgCopyFromStreamCSV !PgCSVCopyFromOptions
+  deriving (Eq, Show)
+
+-- | Stream in using the @text@ format with default options.
+-- Use 'copyFromTextStreamWith' to override.
+--
+-- @since 0.6.1.0
+copyFromTextStream :: PgCopyFromStreamOptions
+copyFromTextStream = PgCopyFromStreamText defaultPgTextCopyFromOptions
+
+-- | Stream in using the @text@ format with the given options.
+--
+-- @since 0.6.1.0
+copyFromTextStreamWith :: PgTextCopyFromOptions -> PgCopyFromStreamOptions
+copyFromTextStreamWith = PgCopyFromStreamText
+
+-- | Stream in using the @csv@ format with default options.
+-- Use 'copyFromCSVStreamWith' to override.
+--
+-- @since 0.6.1.0
+copyFromCSVStream :: PgCopyFromStreamOptions
+copyFromCSVStream = PgCopyFromStreamCSV defaultPgCSVCopyFromOptions
+
+-- | Stream in using the @csv@ format with the given options.
+--
+-- @since 0.6.1.0
+copyFromCSVStreamWith :: PgCSVCopyFromOptions -> PgCopyFromStreamOptions
+copyFromCSVStreamWith = PgCopyFromStreamCSV
+
+-- | Render the @WITH (FORMAT ..., ...)@ tail of a streaming
+-- @COPY ... TO STDOUT@ statement.
+--
+-- @since 0.6.1.0
+emitPgCopyToStreamOptions :: PgCopyToStreamOptions -> PgSyntax
+emitPgCopyToStreamOptions (PgCopyToStreamText o) = emitOptionList (emit "text") (textCopyToFields o)
+emitPgCopyToStreamOptions (PgCopyToStreamCSV o) = emitOptionList (emit "csv") (csvCopyToFields o)
+
+-- | Render the @WITH (FORMAT ..., ...)@ tail of a streaming
+-- @COPY ... FROM STDIN@ statement.
+--
+-- @since 0.6.1.0
+emitPgCopyFromStreamOptions :: PgCopyFromStreamOptions -> PgSyntax
+emitPgCopyFromStreamOptions (PgCopyFromStreamText o) = emitOptionList (emit "text") (textCopyFromFields o)
+emitPgCopyFromStreamOptions (PgCopyFromStreamCSV o) = emitOptionList (emit "csv") (csvCopyFromFields o)
diff --git a/Database/Beam/Postgres/Extensions/Internal.hs b/Database/Beam/Postgres/Extensions/Internal.hs
deleted file mode 100644
--- a/Database/Beam/Postgres/Extensions/Internal.hs
+++ /dev/null
@@ -1,17 +0,0 @@
-module Database.Beam.Postgres.Extensions.Internal where
-
-import Data.Text (Text)
-
-import Database.Beam
-import Database.Beam.Backend.SQL
-import Database.Beam.Postgres
-
-type PgExpr ctxt s = QGenExpr ctxt Postgres s
-
-type family LiftPg ctxt s fn where
-  LiftPg ctxt s (Maybe a -> b) = Maybe (PgExpr ctxt s a) -> LiftPg ctxt s b
-  LiftPg ctxt s (a -> b) = PgExpr ctxt s a -> LiftPg ctxt s b
-  LiftPg ctxt s a = PgExpr ctxt s a
-
-funcE :: IsSql99ExpressionSyntax expr => Text -> [expr] -> expr
-funcE nm args = functionCallE (fieldE (unqualifiedField nm)) args
diff --git a/Database/Beam/Postgres/Extensions/UuidOssp.hs b/Database/Beam/Postgres/Extensions/UuidOssp.hs
--- a/Database/Beam/Postgres/Extensions/UuidOssp.hs
+++ b/Database/Beam/Postgres/Extensions/UuidOssp.hs
@@ -10,8 +10,7 @@
 import           Data.UUID.Types (UUID)
 
 import           Database.Beam
-import           Database.Beam.Postgres.Extensions
-import           Database.Beam.Postgres.Extensions.Internal
+import           Database.Beam.Postgres.Extensions ( LiftPg, IsPgExtension(..), funcE )
 
 -- | Data type representing definitions contained in the @uuid-ossp@ extension
 data UuidOssp = UuidOssp
diff --git a/Database/Beam/Postgres/Full.hs b/Database/Beam/Postgres/Full.hs
--- a/Database/Beam/Postgres/Full.hs
+++ b/Database/Beam/Postgres/Full.hs
@@ -2,7 +2,6 @@
 {-# LANGUAGE UndecidableInstances #-}
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE TupleSections #-}
-{-# LANGUAGE CPP #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
 {-# LANGUAGE TypeOperators #-}
 
@@ -71,6 +70,8 @@
 import           Control.Monad.State.Strict (evalState)
 import           Control.Monad.Writer (runWriterT)
 
+import           Data.List.NonEmpty (nonEmpty)
+import qualified Data.List.NonEmpty as NonEmpty
 import           Data.Kind (Type)
 import           Data.Proxy (Proxy(..))
 import qualified Data.Text as T
@@ -289,18 +290,21 @@
 --
 -- @beam-core@ offers 'selectWith' to produce a top-level 'SqlSelect'
 -- but these cannot be turned into 'Q' objects for use within joins.
---
--- The 'pgSelectWith' function is more flexible and indeed
--- 'selectWith' for @beam-postgres@ is equivalent to se
+-- The 'pgSelectWith' function is more flexible.
 pgSelectWith :: forall db s res
               . Projectible Postgres res
              => With Postgres db (Q Postgres db s res) -> Q Postgres db s res
 pgSelectWith (CTE.With mkQ) =
-    let (q, (recursiveness, ctes)) = evalState (runWriterT mkQ) 0
+    let (q, (recursiveness, mctes)) = evalState (runWriterT mkQ) 0
         fromSyntax tblPfx =
-            case recursiveness of
-              CTE.Nonrecursive -> withSyntax ctes (buildSqlQuery tblPfx q)
-              CTE.Recursive -> withRecursiveSyntax ctes (buildSqlQuery tblPfx q)
+            case (recursiveness, nonEmpty mctes) of
+              (CTE.Nonrecursive, Just ctes) -> withSyntax (NonEmpty.toList ctes) (buildSqlQuery tblPfx q)
+              (CTE.Recursive, Just ctes) -> withRecursiveSyntax (NonEmpty.toList ctes) (buildSqlQuery tblPfx q)
+               -- If there are no subqueries, we don't want to generate
+               -- an empty 'WITH' statement, which would be malformed.
+               -- 
+               -- see: https://github.com/haskell-beam/beam/issues/760
+              (_, Nothing) -> buildSqlQuery tblPfx q
     in Q (liftF (QAll (\tblPfx tName ->
                            let (_, names) = mkFieldNames @Postgres @res (qualifiedField tName)
                            in fromTable (PgTableSourceSyntax $
@@ -309,7 +313,7 @@
                       (\tName ->
                            let (projection, _) = mkFieldNames @Postgres @res (qualifiedField tName)
                            in projection)
-                      (\_ -> Nothing)
+                      (const Nothing)
                       snd))
 
 -- | By default, Postgres will throw an error when a conflict is detected. This
diff --git a/Database/Beam/Postgres/Migrate.hs b/Database/Beam/Postgres/Migrate.hs
--- a/Database/Beam/Postgres/Migrate.hs
+++ b/Database/Beam/Postgres/Migrate.hs
@@ -60,7 +60,7 @@
 import           Control.Exception.Lifted (mask, onException)
 import           Control.Monad
 
-import           Data.Aeson hiding (json)
+import           Data.Aeson
 import           Data.Bits
 import           Data.ByteString (ByteString)
 import qualified Data.ByteString.Lazy as BL
@@ -598,5 +598,11 @@
   field' _ _ nm ty _ collation constraints PgHasDefault =
     Db.field' (Proxy @'True) (Proxy @'False) nm ty Nothing collation constraints
 
-instance BeamSqlBackendHasSerial Postgres where
+instance BeamSqlBackendHasSerial Int16 Postgres where
+  genericSerial nm = Db.field nm smallserial PgHasDefault
+
+instance BeamSqlBackendHasSerial Int32 Postgres where
   genericSerial nm = Db.field nm serial PgHasDefault
+
+instance BeamSqlBackendHasSerial Int64 Postgres where
+  genericSerial nm = Db.field nm bigserial PgHasDefault
diff --git a/Database/Beam/Postgres/PgCrypto.hs b/Database/Beam/Postgres/PgCrypto.hs
--- a/Database/Beam/Postgres/PgCrypto.hs
+++ b/Database/Beam/Postgres/PgCrypto.hs
@@ -9,8 +9,7 @@
 import Database.Beam
 import Database.Beam.Backend.SQL
 
-import Database.Beam.Postgres.Extensions
-import Database.Beam.Postgres.Extensions.Internal
+import Database.Beam.Postgres.Extensions( LiftPg, PgExpr, IsPgExtension(..), funcE )
 
 import Data.Int
 import Data.Text (Text)
diff --git a/Database/Beam/Postgres/PgSpecific.hs b/Database/Beam/Postgres/PgSpecific.hs
--- a/Database/Beam/Postgres/PgSpecific.hs
+++ b/Database/Beam/Postgres/PgSpecific.hs
@@ -9,7 +9,6 @@
 {-# LANGUAGE TypeApplications #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE PolyKinds #-}
-{-# LANGUAGE CPP #-}
 
 -- | Postgres-specific types, functions, and operators
 module Database.Beam.Postgres.PgSpecific
@@ -111,7 +110,7 @@
 
     -- * Postgres @EXTRACT@ fields
   , century_, decade_, dow_, doy_, epoch_, isodow_, isoyear_
-  , microseconds_, milliseconds_, millennium_, quarter_, week_
+  , microseconds_, milliseconds_, millennium_, quarter_
 
     -- ** Postgres functions and aggregates
   , pgBoolOr, pgBoolAnd, pgStringAgg, pgStringAggOver
@@ -1674,9 +1673,6 @@
 
 quarter_ :: HasSqlDate tgt => ExtractField Postgres tgt Int32
 quarter_ = ExtractField (PgExtractFieldSyntax (emit "QUARTER"))
-
-week_ :: HasSqlDate tgt => ExtractField Postgres tgt Int32
-week_ = ExtractField (PgExtractFieldSyntax (emit "WEEK"))
 
 -- $full-text-search
 --
diff --git a/Database/Beam/Postgres/Syntax.hs b/Database/Beam/Postgres/Syntax.hs
--- a/Database/Beam/Postgres/Syntax.hs
+++ b/Database/Beam/Postgres/Syntax.hs
@@ -22,7 +22,7 @@
     , emit, emitBuilder, escapeString
     , escapeBytea, escapeIdentifier
     , pgParens
-
+    , pgStringLit, pgCharLit, pgBoolLit
     , nextSyntaxStep
 
     , PgCommandSyntax(..), PgCommandType(..)
@@ -131,6 +131,8 @@
 import qualified Database.PostgreSQL.Simple.Types as Pg (Oid(..), Binary(..), Null(..))
 import qualified Database.PostgreSQL.Simple.Time as Pg (Date, LocalTimestamp, UTCTimestamp)
 import qualified Database.PostgreSQL.Simple.HStore as Pg (HStoreList, HStoreMap, HStoreBuilder)
+import Data.Text (Text)
+import qualified Data.ByteString.Char8 as BS8
 
 data PostgresInaccessible
 
@@ -798,6 +800,7 @@
   minutesField = PgExtractFieldSyntax (emit "MINUTE")
   hourField    = PgExtractFieldSyntax (emit "HOUR")
   dayField     = PgExtractFieldSyntax (emit "DAY")
+  weekField    = PgExtractFieldSyntax (emit "WEEK")
   monthField   = PgExtractFieldSyntax (emit "MONTH")
   yearField    = PgExtractFieldSyntax (emit "YEAR")
 
@@ -1388,6 +1391,27 @@
 
 pgParens :: PgSyntax -> PgSyntax
 pgParens a = emit "(" <> a <> emit ")"
+
+-- | Render a 'Text' as a single-quoted SQL string literal, with proper
+-- Postgres escaping. The surrounding quotes are added here; 'escapeString'
+-- only handles the escaping of the contents.
+--
+-- @since 0.6.1.0
+pgStringLit :: Text -> PgSyntax
+pgStringLit t = emit "'" <> escapeString (TE.encodeUtf8 t) <> emit "'"
+
+-- | Render a 'Char' as a single-quoted SQL string literal.
+--
+-- @since 0.6.1.0
+pgCharLit :: Char -> PgSyntax
+pgCharLit c = emit "'" <> escapeString (BS8.singleton c) <> emit "'"
+
+-- | Render a boolean as the literal @TRUE@ or @FALSE@.
+--
+-- @since 0.6.1.0
+pgBoolLit :: Bool -> PgSyntax
+pgBoolLit True = emit "TRUE"
+pgBoolLit False = emit "FALSE"
 
 pgTableOp :: ByteString -> PgSelectTableSyntax -> PgSelectTableSyntax
           -> PgSelectTableSyntax
diff --git a/Database/Beam/Postgres/Types.hs b/Database/Beam/Postgres/Types.hs
--- a/Database/Beam/Postgres/Types.hs
+++ b/Database/Beam/Postgres/Types.hs
@@ -1,5 +1,5 @@
 {-# OPTIONS_GHC -fno-warn-orphans #-}
-
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE UndecidableInstances #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
@@ -18,8 +18,18 @@
 import           Database.Beam
 import           Database.Beam.Backend
 import           Database.Beam.Backend.Internal.Compat
+import           Database.Beam.Backend.SQL.BeamExtensions
+                   ( BeamSqlBackendCopyFromStreamSyntax
+                   , BeamSqlBackendCopyFromSyntax
+                   , BeamSqlBackendCopyToStreamSyntax
+                   , BeamSqlBackendCopyToSyntax
+                   )
 import           Database.Beam.Migrate.Generics
 import           Database.Beam.Migrate.SQL (BeamMigrateOnlySqlBackend)
+import           Database.Beam.Postgres.Extensions.Copy.File
+                   ( PgCopyFromSyntax, PgCopyToSyntax )
+import           Database.Beam.Postgres.Extensions.Copy.Stream
+                   ( PgCopyFromStreamSyntax, PgCopyToStreamSyntax )
 import           Database.Beam.Postgres.Syntax
 import           Database.Beam.Query.SQL92
 
@@ -166,8 +176,20 @@
 instance BeamMigrateOnlySqlBackend Postgres
 type instance BeamSqlBackendSyntax Postgres = PgCommandSyntax
 
+type instance BeamSqlBackendCopyToSyntax Postgres = PgCopyToSyntax
+type instance BeamSqlBackendCopyFromSyntax Postgres = PgCopyFromSyntax
+
+type instance BeamSqlBackendCopyToStreamSyntax Postgres = PgCopyToStreamSyntax
+type instance BeamSqlBackendCopyFromStreamSyntax Postgres = PgCopyFromStreamSyntax
+
 instance BeamSqlBackendIsString Postgres String
 instance BeamSqlBackendIsString Postgres Text
+
+-- | @since 0.6.2.0
+instance BeamSqlBackendIsString Postgres (CI String)
+
+-- | @since 0.6.2.0
+instance BeamSqlBackendIsString Postgres (CI Text)
 
 instance HasQBuilder Postgres where
   buildSqlQuery = buildSql92Query' True
diff --git a/beam-postgres.cabal b/beam-postgres.cabal
--- a/beam-postgres.cabal
+++ b/beam-postgres.cabal
@@ -1,5 +1,5 @@
 name:                 beam-postgres
-version:              0.5.6.1
+version:              0.6.2.0
 synopsis:             Connection layer between beam and postgres
 description:          Beam driver for <https://www.postgresql.org/ PostgreSQL>, an advanced open-source RDBMS
 homepage:             https://haskell-beam.github.io/beam/user-guide/backends/beam-postgres
@@ -23,20 +23,21 @@
                       Database.Beam.Postgres.Full
 
                       Database.Beam.Postgres.PgCrypto
+                      Database.Beam.Postgres.Extensions
                       Database.Beam.Postgres.Extensions.UuidOssp
 
                       Database.Beam.Postgres.TempTable
 
   other-modules:      Database.Beam.Postgres.Connection
                       Database.Beam.Postgres.Debug
-                      Database.Beam.Postgres.Extensions
-                      Database.Beam.Postgres.Extensions.Internal
+                      Database.Beam.Postgres.Extensions.Copy.File
+                      Database.Beam.Postgres.Extensions.Copy.Stream
                       Database.Beam.Postgres.PgSpecific
                       Database.Beam.Postgres.Types
 
   build-depends:      base                 >=4.11 && <5.0,
-                      beam-core            >=0.10 && <0.11,
-                      beam-migrate         >=0.5.4.0 && <0.6,
+                      beam-core            >=0.11.1 && <0.12,
+                      beam-migrate         >=0.6 && <0.7,
 
                       postgresql-libpq     >=0.8  && <0.12,
                       postgresql-simple    >=0.5  && <0.8,
@@ -48,11 +49,11 @@
                       hashable             >=1.1  && <1.6,
                       lifted-base          >=0.2  && <0.3,
                       free                 >=4.12 && <5.3,
-                      time                 >=1.6  && <1.15,
+                      time                 >=1.6  && <1.17,
                       monad-control        >=1.0  && <1.1,
                       mtl                  >=2.1  && <2.4,
                       conduit              >=1.2  && <1.4,
-                      aeson                >=0.11 && <2.3,
+                      aeson                >=0.11 && <2.4,
                       uuid-types           >=1.0  && <1.1,
                       case-insensitive     >=1.2  && <1.3,
                       scientific           >=0.3  && <0.4,
@@ -65,7 +66,7 @@
   default-language:   Haskell2010
   default-extensions: ScopedTypeVariables, OverloadedStrings, MultiParamTypeClasses, RankNTypes, FlexibleInstances,
                       DeriveDataTypeable, DeriveGeneric, StandaloneDeriving, TypeFamilies, GADTs, OverloadedStrings,
-                      CPP, TypeApplications, FlexibleContexts
+                      TypeApplications, FlexibleContexts
   ghc-options:        -Wall
                       -Widentities
                       -Wincomplete-uni-patterns
@@ -80,11 +81,14 @@
   hs-source-dirs: test
   main-is: Main.hs
   other-modules: Database.Beam.Postgres.Test,
+                 Database.Beam.Postgres.Test.Copy,
                  Database.Beam.Postgres.Test.Marshal,
                  Database.Beam.Postgres.Test.Select,
+                 Database.Beam.Postgres.Test.Select.PgNubBy,
                  Database.Beam.Postgres.Test.DataTypes,
                  Database.Beam.Postgres.Test.Migrate,
-                 Database.Beam.Postgres.Test.TempTable
+                 Database.Beam.Postgres.Test.TempTable,
+                 Database.Beam.Postgres.Test.Windowing
   build-depends:
     aeson,
     base,
@@ -92,12 +96,13 @@
     beam-migrate,
     beam-postgres,
     bytestring,
-    hedgehog,
+    hedgehog >= 1.0,
     postgresql-simple,
     tasty-hunit,
     tasty,
     text,
     testcontainers,
+    time,
     uuid,
     vector
   default-language: Haskell2010
diff --git a/test/Database/Beam/Postgres/Test.hs b/test/Database/Beam/Postgres/Test.hs
--- a/test/Database/Beam/Postgres/Test.hs
+++ b/test/Database/Beam/Postgres/Test.hs
@@ -1,10 +1,5 @@
-{-# LANGUAGE CPP #-}
 module Database.Beam.Postgres.Test where
 
-#if MIN_VERSION_base(4,12,0)
-import           Prelude hiding (fail)
-#endif
-
 import qualified Database.PostgreSQL.Simple as Pg
 
 import           Control.Exception (bracket)
@@ -13,18 +8,6 @@
 
 import           Data.ByteString (ByteString)
 import           Data.String
-
-#if MIN_VERSION_base(4,12,0)
-#if !MIN_VERSION_hedgehog(1,0,0)
-import           Control.Monad.Fail (MonadFail(..))
-import qualified Hedgehog
--- TODO orphan instances are bad
--- Would be easier to say 'build-depends: hedgehog >= 1.0',
--- but it's difficult to propagate to older Stackage snapshots
-instance Monad m => MonadFail (Hedgehog.PropertyT m) where
-    fail _ = Hedgehog.failure
-#endif
-#endif
 
 withTestPostgres :: String -> IO ByteString -> (Pg.Connection -> IO a) -> IO a
 withTestPostgres dbName getConnStr action = do
diff --git a/test/Database/Beam/Postgres/Test/Copy.hs b/test/Database/Beam/Postgres/Test/Copy.hs
new file mode 100644
--- /dev/null
+++ b/test/Database/Beam/Postgres/Test/Copy.hs
@@ -0,0 +1,444 @@
+{-# LANGUAGE DeriveAnyClass #-}
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE StandaloneDeriving #-}
+{-# LANGUAGE TypeFamilies #-}
+
+module Database.Beam.Postgres.Test.Copy (tests) where
+
+import Control.Monad (void)
+import Control.Monad.IO.Class (liftIO)
+import Data.ByteString (ByteString)
+import qualified Data.ByteString as BS
+import Data.IORef (modifyIORef', newIORef, readIORef, writeIORef)
+import Data.Int (Int32)
+import Data.List (sort)
+import Data.Text (Text)
+import qualified Data.Text as T
+import Database.Beam
+import Database.Beam.Backend.SQL.BeamExtensions
+  ( MonadBeamCopyFrom (..),
+    MonadBeamCopyFromStream (..),
+    MonadBeamCopyTo (..),
+    MonadBeamCopyToStream (..),
+    copySelectTo,
+    copySelectToStream,
+    copyTableFrom,
+    copyTableFromStream,
+    copyTableTo,
+    copyTableToStream,
+  )
+import Database.Beam.Postgres
+import Database.Beam.Postgres.Test (withTestPostgres)
+import Database.PostgreSQL.Simple (Connection, execute_)
+import Hedgehog ((===))
+import qualified Hedgehog
+import qualified Hedgehog.Gen as Gen
+import qualified Hedgehog.Range as Range
+import Test.Tasty (TestTree, testGroup)
+import Test.Tasty.HUnit (Assertion, assertBool, assertEqual, testCase)
+
+tests :: IO ByteString -> TestTree
+tests getConn =
+  testGroup
+    "COPY statements"
+    [ testGroup
+        "COPY ... TO / ... FROM round-trip"
+        [ testRoundtripCsvAllColumns getConn,
+          testRoundtripCsvMultiColumnProjection getConn,
+          testRoundtripCsvSingleColumnProjection getConn,
+          testRoundtripCsvFromSelect getConn
+        ],
+      testGroup
+        "options"
+        [ testCustomDelimiter getConn,
+          testNoHeader getConn,
+          testTextFormat getConn
+        ],
+      testGroup
+        "streaming COPY"
+        [ testStreamRoundtripCsv getConn,
+          testStreamFromSelect getConn
+        ],
+      testGroup
+        "property-based round-trip"
+        [ testPropCsvRoundtrip getConn,
+          testPropTextRoundtrip getConn
+        ]
+    ]
+
+-- | The full table is exported to a CSV, the table is truncated, and the CSV
+-- is re-imported. The final rows must match the original ones.
+testRoundtripCsvAllColumns :: IO ByteString -> TestTree
+testRoundtripCsvAllColumns getConn =
+  testCopy getConn "copy_all_columns_csv" "/tmp/copy_all_columns.csv" $ \conn path -> do
+    seedWidgets conn widgetData
+    runBeamPostgres conn $ do
+      runCopyTo $ copyTableTo (_dbWidgets testDb) id (copyToCSV path)
+    truncateWidgets conn
+    runBeamPostgres conn $ do
+      runCopyFrom $ copyTableFrom (_dbWidgets testDb) id (copyFromCSV path)
+    rows <- queryAllWidgets conn
+    assertEqual "round-tripped rows match seed" widgetData rows
+
+-- | Project a subset of columns; the unprojected column gets its DEFAULT on
+-- import.
+testRoundtripCsvMultiColumnProjection :: IO ByteString -> TestTree
+testRoundtripCsvMultiColumnProjection getConn =
+  testCopy getConn "copy_multi_column_csv" "/tmp/copy_multi_column.csv" $ \conn path -> do
+    seedWidgets conn widgetData
+    runBeamPostgres conn $ do
+      runCopyTo $
+        copyTableTo
+          (_dbWidgets testDb)
+          (\w -> (_widgetId w, _widgetName w))
+          (copyToCSV path)
+    truncateWidgets conn
+    runBeamPostgres conn $ do
+      runCopyFrom $
+        copyTableFrom
+          (_dbWidgets testDb)
+          (\w -> (_widgetId w, _widgetName w))
+          (copyFromCSV path)
+    rows <- queryAllWidgets conn
+    -- 'price' was not in the projection, so it gets its DEFAULT (0).
+    let expected = [w {_widgetPrice = 0} | w <- widgetData]
+    assertEqual "id+name round-tripped, price defaulted" expected rows
+
+-- | Single-column projection.
+testRoundtripCsvSingleColumnProjection :: IO ByteString -> TestTree
+testRoundtripCsvSingleColumnProjection getConn =
+  testCopy getConn "copy_single_column_csv" "/tmp/copy_single_column.csv" $ \conn path -> do
+    seedWidgets conn widgetData
+    runBeamPostgres conn $ do
+      runCopyTo $ copyTableTo (_dbWidgets testDb) _widgetId (copyToCSV path)
+    truncateWidgets conn
+    runBeamPostgres conn $ do
+      runCopyFrom $ copyTableFrom (_dbWidgets testDb) _widgetId (copyFromCSV path)
+    rows <- queryAllWidgets conn
+    let expected = [w {_widgetName = "", _widgetPrice = 0} | w <- widgetData]
+    assertEqual "id-only round-tripped, name+price defaulted" expected rows
+
+-- | Use copySelectTo with a filtered query, then COPY FROM the result back
+-- into the table.
+testRoundtripCsvFromSelect :: IO ByteString -> TestTree
+testRoundtripCsvFromSelect getConn =
+  testCopy getConn "copy_select_csv" "/tmp/copy_select.csv" $ \conn path -> do
+    seedWidgets conn widgetData
+    runBeamPostgres conn $ do
+      runCopyTo $
+        copySelectTo
+          ( select $ do
+              w <- all_ (_dbWidgets testDb)
+              guard_ (_widgetPrice w >. val_ 4.0)
+              pure w
+          )
+          (copyToCSV path)
+    truncateWidgets conn
+    runBeamPostgres conn $ do
+      runCopyFrom $ copyTableFrom (_dbWidgets testDb) id (copyFromCSV path)
+    rows <- queryAllWidgets conn
+    -- Only Widget (9.99) and Sprocket (4.5) have price > 4.0; Cog is excluded.
+    let expected = sort [w | w <- widgetData, _widgetPrice w > 4.0]
+    assertEqual "select-filtered round-trip" expected rows
+
+-- | Use a custom delimiter on both sides of the round-trip.
+testCustomDelimiter :: IO ByteString -> TestTree
+testCustomDelimiter getConn =
+  testCopy getConn "copy_custom_delim_csv" "/tmp/copy_custom_delim.csv" $ \conn path -> do
+    seedWidgets conn widgetData
+    let toOpts = copyToCSVWith path defaultPgCSVCopyToOptions {pgCsvCopyToDelimiter = Just '|'}
+        fromOpts = copyFromCSVWith path defaultPgCSVCopyFromOptions {pgCsvCopyFromDelimiter = Just '|'}
+    runBeamPostgres conn $ do
+      runCopyTo $ copyTableTo (_dbWidgets testDb) id toOpts
+    truncateWidgets conn
+    runBeamPostgres conn $ do
+      runCopyFrom $ copyTableFrom (_dbWidgets testDb) id fromOpts
+    rows <- queryAllWidgets conn
+    assertEqual "round-trip with '|' delimiter" widgetData rows
+
+-- | Toggle HEADER off on TO and on on FROM; round-trip should still work
+-- (as long as both sides agree).
+testNoHeader :: IO ByteString -> TestTree
+testNoHeader getConn =
+  testCopy getConn "copy_no_header_csv" "/tmp/copy_no_header.csv" $ \conn path -> do
+    seedWidgets conn widgetData
+    let toOpts = copyToCSVWith path defaultPgCSVCopyToOptions {pgCsvCopyToHeader = Just False}
+        fromOpts = copyFromCSVWith path defaultPgCSVCopyFromOptions {pgCsvCopyFromHeader = Just False}
+    runBeamPostgres conn $ do
+      runCopyTo $ copyTableTo (_dbWidgets testDb) id toOpts
+    truncateWidgets conn
+    runBeamPostgres conn $ do
+      runCopyFrom $ copyTableFrom (_dbWidgets testDb) id fromOpts
+    rows <- queryAllWidgets conn
+    assertEqual "round-trip without header line" widgetData rows
+
+-- | The 'text' format with custom delimiter, round-tripped.
+testTextFormat :: IO ByteString -> TestTree
+testTextFormat getConn =
+  testCopy getConn "copy_text_format" "/tmp/copy_text.txt" $ \conn path -> do
+    seedWidgets conn widgetData
+    let toOpts = copyToTextWith path defaultPgTextCopyToOptions {pgTextCopyToDelimiter = Just '\t'}
+        fromOpts = copyFromTextWith path defaultPgTextCopyFromOptions {pgTextCopyFromDelimiter = Just '\t'}
+    runBeamPostgres conn $ do
+      runCopyTo $ copyTableTo (_dbWidgets testDb) id toOpts
+    truncateWidgets conn
+    runBeamPostgres conn $ do
+      runCopyFrom $ copyTableFrom (_dbWidgets testDb) id fromOpts
+    rows <- queryAllWidgets conn
+    assertEqual "round-trip via text format" widgetData rows
+
+-- | Round-trip widgets through streaming @COPY ... TO STDOUT@ then
+-- @COPY ... FROM STDIN@. The bytes pass through the client connection only;
+-- no server-side file is touched.
+testStreamRoundtripCsv :: IO ByteString -> TestTree
+testStreamRoundtripCsv getConn =
+  testCopy getConn "stream_roundtrip_csv" "" $ \conn _ -> do
+    seedWidgets conn widgetData
+    -- Drain the stream into an IORef.
+    chunksRef <- newIORef []
+    runBeamPostgres conn $
+      runCopyToStream
+        (copyTableToStream (_dbWidgets testDb) id copyToCSVStream)
+        (\chunk -> modifyIORef' chunksRef (chunk :))
+    payload <- BS.concat . reverse <$> readIORef chunksRef
+    assertBool "stream produced non-empty payload" (not (BS.null payload))
+    -- Replay the captured bytes back into the table.
+    truncateWidgets conn
+    sourceRef <- newIORef (Just payload)
+    runBeamPostgres conn $
+      runCopyFromStream
+        (copyTableFromStream (_dbWidgets testDb) id copyFromCSVStream)
+        ( do
+            mchunk <- readIORef sourceRef
+            writeIORef sourceRef Nothing
+            pure mchunk
+        )
+    rows <- queryAllWidgets conn
+    assertEqual "round-tripped rows match seed" widgetData rows
+
+-- | @COPY (SELECT ...) TO STDOUT@ via 'copySelectToStream'.
+testStreamFromSelect :: IO ByteString -> TestTree
+testStreamFromSelect getConn =
+  testCopy getConn "stream_from_select" "" $ \conn _ -> do
+    seedWidgets conn widgetData
+    chunksRef <- newIORef []
+    runBeamPostgres conn $
+      runCopyToStream
+        ( copySelectToStream
+            ( select $ do
+                w <- all_ (_dbWidgets testDb)
+                guard_ (_widgetPrice w >. val_ 4.0)
+                pure w
+            )
+            copyToCSVStream
+        )
+        (\chunk -> modifyIORef' chunksRef (chunk :))
+    payload <- BS.concat . reverse <$> readIORef chunksRef
+    -- The payload should mention the two widgets with price > 4.0 and not
+    -- the one priced 1.25.
+    assertBool "Widget present" ("Widget" `BS.isInfixOf` payload)
+    assertBool "Sprocket present" ("Sprocket" `BS.isInfixOf` payload)
+    assertBool "Cog absent" (not ("Cog" `BS.isInfixOf` payload))
+
+testPropCsvRoundtrip :: IO ByteString -> TestTree
+testPropCsvRoundtrip getConn =
+  testCopy getConn "prop_csv_roundtrip" "/tmp/prop_csv.csv" $ \conn path -> do
+    passes <-
+      Hedgehog.check . Hedgehog.property $ do
+        toOpts <- Hedgehog.forAll genCsvToOpts
+        let fromOpts = matchedCsvFromOpts toOpts
+        rows <-
+          liftIO $
+            roundtripWidgets conn $ \c -> do
+              runBeamPostgres c $
+                runCopyTo $
+                  copyTableTo (_dbWidgets testDb) id (copyToCSVWith path toOpts)
+              truncateWidgets c
+              runBeamPostgres c $
+                runCopyFrom $
+                  copyTableFrom (_dbWidgets testDb) id (copyFromCSVWith path fromOpts)
+        rows === widgetData
+    assertBool "Hedgehog property failed" passes
+  where
+    genCsvToOpts = do
+      delim <- Gen.maybe genDelimiterChar
+      hdr <- Gen.maybe Gen.bool
+      quote <- Gen.maybe genQuoteChar
+      escape <- Gen.maybe genEscapeChar
+      nullStr <- Gen.maybe genNullStr
+      pure
+        defaultPgCSVCopyToOptions
+          { pgCsvCopyToDelimiter = delim,
+            pgCsvCopyToHeader = hdr,
+            pgCsvCopyToQuote = quote,
+            pgCsvCopyToEscape = escape,
+            pgCsvCopyToNullStr = nullStr
+          }
+
+    matchedCsvFromOpts :: PgCSVCopyToOptions -> PgCSVCopyFromOptions
+    matchedCsvFromOpts o =
+      defaultPgCSVCopyFromOptions
+        { pgCsvCopyFromDelimiter = pgCsvCopyToDelimiter o,
+          pgCsvCopyFromHeader = pgCsvCopyToHeader o,
+          pgCsvCopyFromQuote = pgCsvCopyToQuote o,
+          pgCsvCopyFromEscape = pgCsvCopyToEscape o,
+          pgCsvCopyFromNullStr = pgCsvCopyToNullStr o
+        }
+
+testPropTextRoundtrip :: IO ByteString -> TestTree
+testPropTextRoundtrip getConn =
+  testCopy getConn "prop_text_roundtrip" "/tmp/prop_text.txt" $ \conn path -> do
+    passes <-
+      Hedgehog.check . Hedgehog.property $ do
+        toOpts <- Hedgehog.forAll genTextToOpts
+        let fromOpts = matchedTextFromOpts toOpts
+        rows <-
+          liftIO $
+            roundtripWidgets conn $ \c -> do
+              runBeamPostgres c $
+                runCopyTo $
+                  copyTableTo (_dbWidgets testDb) id (copyToTextWith path toOpts)
+              truncateWidgets c
+              runBeamPostgres c $
+                runCopyFrom $
+                  copyTableFrom (_dbWidgets testDb) id (copyFromTextWith path fromOpts)
+        rows === widgetData
+    assertBool "Hedgehog property failed" passes
+  where
+    genTextToOpts = do
+      delim <- Gen.maybe genDelimiterChar
+      hdr <- Gen.maybe Gen.bool
+      -- Avoid generating a NULL string that contains the chosen delimiter.
+      nullStr <- Gen.maybe (Gen.filter (not . T.any (== ',')) genNullStr)
+      pure
+        defaultPgTextCopyToOptions
+          { pgTextCopyToDelimiter = delim,
+            pgTextCopyToHeader = hdr,
+            pgTextCopyToNullStr = nullStr
+          }
+
+    -- \| Mirror of 'matchedCsvFromOpts' for the @text@ format. 'pgTextCopyFromFreeze'
+    -- is intentionally left at @Nothing@: PostgreSQL only accepts @FREEZE@ when
+    -- the target table has not been touched in the current (sub)transaction, but
+    -- our property test truncates before the FROM, which violates that
+    -- precondition.
+    matchedTextFromOpts :: PgTextCopyToOptions -> PgTextCopyFromOptions
+    matchedTextFromOpts o =
+      defaultPgTextCopyFromOptions
+        { pgTextCopyFromDelimiter = pgTextCopyToDelimiter o,
+          pgTextCopyFromHeader = pgTextCopyToHeader o,
+          pgTextCopyFromNullStr = pgTextCopyToNullStr o
+        }
+
+-- Single-byte delimiters that never appear in 'widgetData'. Avoiding @.@
+-- matters for the @text@ format because the data contains floating-point
+-- prices like @9.99@.
+genDelimiterChar :: Hedgehog.Gen Char
+genDelimiterChar = Gen.element [',', ';', '|', '\t']
+
+genQuoteChar :: Hedgehog.Gen Char
+genQuoteChar = Gen.element ['"', '\'']
+
+genEscapeChar :: Hedgehog.Gen Char
+genEscapeChar = Gen.element ['"', '\'', '\\']
+
+genNullStr :: Hedgehog.Gen Text
+genNullStr = Gen.element ["NULL", "~~~"]
+
+roundtripWidgets :: Connection -> (Connection -> IO ()) -> IO [Widget]
+roundtripWidgets conn action = do
+  truncateWidgets conn
+  seedWidgets conn widgetData
+  action conn
+  queryAllWidgets conn
+
+testCopy ::
+  IO ByteString ->
+  String ->
+  -- | Server-side file path inside the Postgres container.
+  FilePath ->
+  (Connection -> FilePath -> Assertion) ->
+  TestTree
+testCopy getConn name path action = testCase name $
+  withTestPostgres name getConn $ \conn -> do
+    createWidgetsTable conn
+    action conn path
+
+queryAllWidgets :: Connection -> IO [Widget]
+queryAllWidgets conn =
+  runBeamPostgres conn $
+    runSelectReturningList $
+      select $
+        orderBy_ (asc_ . _widgetId) $
+          all_ (_dbWidgets testDb)
+
+createWidgetsTable :: Connection -> IO ()
+createWidgetsTable conn =
+  void $
+    execute_
+      conn
+      "CREATE TABLE widgets (\
+      \  id INTEGER PRIMARY KEY,\
+      \  name TEXT NOT NULL DEFAULT '',\
+      \  price DOUBLE PRECISION NOT NULL DEFAULT 0\
+      \)"
+
+truncateWidgets :: Connection -> IO ()
+truncateWidgets conn = void $ execute_ conn "TRUNCATE TABLE widgets"
+
+seedWidgets :: Connection -> [Widget] -> IO ()
+seedWidgets conn widgets =
+  runBeamPostgres conn $
+    runInsert $
+      insert (_dbWidgets testDb) (insertValues widgets)
+
+widgetData :: [Widget]
+widgetData =
+  [ Widget 1 "Widget" 9.99,
+    Widget 2 "Sprocket" 4.50,
+    Widget 3 "Cog" 1.25
+  ]
+
+data WidgetT f = Widget
+  { _widgetId :: Columnar f Int32,
+    _widgetName :: Columnar f Text,
+    _widgetPrice :: Columnar f Double
+  }
+  deriving (Generic)
+
+type Widget = WidgetT Identity
+
+deriving instance Show Widget
+
+deriving instance Eq Widget
+
+deriving instance Ord Widget
+
+instance Beamable WidgetT
+
+instance Table WidgetT where
+  data PrimaryKey WidgetT f = WidgetId (Columnar f Int32)
+    deriving (Generic)
+  primaryKey = WidgetId . _widgetId
+
+instance Beamable (PrimaryKey WidgetT)
+
+newtype TestDB f = TestDB
+  { _dbWidgets :: f (TableEntity WidgetT)
+  }
+  deriving (Generic, Database be)
+
+testDb :: DatabaseSettings Postgres TestDB
+testDb =
+  defaultDbSettings
+    `withDbModification` dbModification
+      { _dbWidgets =
+          modifyTableFields
+            tableModification
+              { _widgetId = "id",
+                _widgetName = "name",
+                _widgetPrice = "price"
+              }
+      }
diff --git a/test/Database/Beam/Postgres/Test/DataTypes.hs b/test/Database/Beam/Postgres/Test/DataTypes.hs
--- a/test/Database/Beam/Postgres/Test/DataTypes.hs
+++ b/test/Database/Beam/Postgres/Test/DataTypes.hs
@@ -3,10 +3,10 @@
 module Database.Beam.Postgres.Test.DataTypes where
 
 import Database.Beam
+import Database.Beam.Backend.SQL.BeamExtensions
+import Database.Beam.Migrate
 import Database.Beam.Postgres
 import Database.Beam.Postgres.Test
-import Database.Beam.Migrate
-import Database.Beam.Backend.SQL.BeamExtensions
 
 import Control.Exception (SomeException(..), handle)
 
@@ -141,15 +141,15 @@
 -- | Regression test for <https://github.com/haskell-beam/beam/issues/700>
 errorOnLiteralDoubles :: IO ByteString -> TestTree
 errorOnLiteralDoubles pgConn =
-    testCase "Literal `Double`s are correctly specified as SQL `DOUBLE` (#700)" $ 
+    testCase "Literal `Double`s are correctly specified as SQL `DOUBLE` (#700)" $
     withTestPostgres "db_failures" pgConn $ \conn -> do
-      results <- runBeamPostgres conn $ 
-        runSelectReturningList $ 
-          select $ 
+      results <- runBeamPostgres conn $
+        runSelectReturningList $
+          select $
             query
-      
+
       results @?= [(99 :: Int32, 1.0 :: Double)]
-    
+
     where
       -- We need to provide a db for type-checking, but it will not be used
       query :: Q Postgres RealDb s (QExpr Postgres s Int32, QExpr Postgres s Double)
diff --git a/test/Database/Beam/Postgres/Test/Marshal.hs b/test/Database/Beam/Postgres/Test/Marshal.hs
--- a/test/Database/Beam/Postgres/Test/Marshal.hs
+++ b/test/Database/Beam/Postgres/Test/Marshal.hs
@@ -52,7 +52,7 @@
                         (PgPoint (max x1 x2) (max y1 y2)))
 
 arrayGen :: Hedgehog.Gen a -> Hedgehog.Gen (Vector.Vector a)
-arrayGen = fmap Vector.fromList 
+arrayGen = fmap Vector.fromList
          . Gen.list (Range.linear 0 5) -- small arrays == quick tests
 
 boxCmp :: PgBox -> PgBox -> Bool
@@ -100,8 +100,8 @@
 
     -- Arrays
     --
-    -- Testing lots of element types for arrays is important, because 
-    -- the mapping between array Oid and element Oid is not type 
+    -- Testing lots of element types for arrays is important, because
+    -- the mapping between array Oid and element Oid is not type
     -- safe, and hence error-prone.
     , marshalTest (arrayGen textGen) postgresConn
     , marshalTest (arrayGen (Gen.double (Range.exponentialFloat 0 1e40))) postgresConn
diff --git a/test/Database/Beam/Postgres/Test/Select.hs b/test/Database/Beam/Postgres/Test/Select.hs
--- a/test/Database/Beam/Postgres/Test/Select.hs
+++ b/test/Database/Beam/Postgres/Test/Select.hs
@@ -5,6 +5,7 @@
 
 import           Data.Aeson
 import           Data.ByteString (ByteString)
+import           Data.List.NonEmpty (NonEmpty(..))
 import           Data.Int
 import           Data.List (sort)
 import qualified Data.Text as T
@@ -164,7 +165,7 @@
         pgCreateExtension @UuidOssp
       let ext = getPgExtension $ _uuidOssp $ unCheckDatabase db
       runSelectReturningList $ select $ do
-        v <- values_ [val_ nil]
+        v <- values_ (val_ nil :| [])
         return $ pgUuidGenerateV5 ext v ""
     assertEqual "result" [V5.generateNamed nil []] result
 
diff --git a/test/Database/Beam/Postgres/Test/Select/PgNubBy.hs b/test/Database/Beam/Postgres/Test/Select/PgNubBy.hs
new file mode 100644
--- /dev/null
+++ b/test/Database/Beam/Postgres/Test/Select/PgNubBy.hs
@@ -0,0 +1,119 @@
+{-# LANGUAGE DerivingStrategies #-}
+{-# LANGUAGE NamedFieldPuns #-}
+{-# LANGUAGE StandaloneDeriving #-}
+
+module Database.Beam.Postgres.Test.Select.PgNubBy (tests) where
+
+import Control.Monad (void)
+import Data.ByteString (ByteString)
+import Data.Int (Int32)
+import Data.Text (Text)
+import Data.Time.Calendar (Day, fromGregorian)
+import Database.Beam
+import Database.Beam.Migrate (defaultMigratableDbSettings)
+import Database.Beam.Migrate.Simple (autoMigrate)
+import Database.Beam.Postgres
+import Database.Beam.Postgres.Migrate (migrationBackend)
+import Database.Beam.Postgres.Test (withTestPostgres)
+import Test.Tasty
+import Test.Tasty.HUnit
+
+tests :: IO ByteString -> TestTree
+tests getConn =
+  testGroup
+    "pgNubBy_ / nub_ with window functions (issue #746)"
+    [ testPgNubByWithLead getConn,
+      testNubWithLead getConn
+    ]
+
+-- Reproducer for issue #746
+testPgNubByWithLead :: IO ByteString -> TestTree
+testPgNubByWithLead getConn = testCase "pgNubBy_ feeding lead1_" $
+  withTestPostgres "issue_746_pg_nub_by" getConn $ \conn -> do
+    setupDb conn
+    results <-
+      runBeamPostgres conn $
+        runSelectReturningList $
+          select $
+            withWindow_
+              (\vf -> frame_ noPartition_ (orderPartitionBy_ (asc_ vf)) noBounds_)
+              (\vf w -> (vf, lead1_ vf `over_` w))
+              (pgNubBy_ id (validFrom <$> all_ (persons db)))
+
+    let expected =
+          [ (day 2025 1 1, Just (day 2025 1 2)),
+            (day 2025 1 2, Just (day 2025 1 3)),
+            (day 2025 1 3, Nothing)
+          ]
+    assertEqual "lead1_ over pgNubBy_ should pair each distinct date with the next" expected results
+
+-- Reproducer for issue #746 with @nub_@
+testNubWithLead :: IO ByteString -> TestTree
+testNubWithLead getConn = testCase "nub_ feeding lead1_" $
+  withTestPostgres "issue_746_nub" getConn $ \conn -> do
+    setupDb conn
+    results <-
+      runBeamPostgres conn $
+        runSelectReturningList $
+          select $
+            withWindow_
+              (\vf -> frame_ noPartition_ (orderPartitionBy_ (asc_ vf)) noBounds_)
+              (\vf w -> (vf, lead1_ vf `over_` w))
+              (nub_ (validFrom <$> all_ (persons db)))
+
+    let expected =
+          [ (day 2025 1 1, Just (day 2025 1 2)),
+            (day 2025 1 2, Just (day 2025 1 3)),
+            (day 2025 1 3, Nothing)
+          ]
+    assertEqual "lead1_ over nub_ should pair each distinct date with the next" expected results
+
+data PersonT f = Person
+  { name :: C f Text,
+    validFrom :: C f Day,
+    idx :: C f Int32
+  }
+  deriving (Generic)
+
+type Person = PersonT Identity
+
+deriving instance Show Person
+
+deriving instance Eq Person
+
+instance Beamable PersonT
+
+instance Table PersonT where
+  data PrimaryKey PersonT f = PersonKey (C f Text)
+    deriving stock (Generic)
+    deriving anyclass (Beamable)
+
+  primaryKey Person {name} = PersonKey name
+
+newtype Db f = Db
+  { persons :: f (TableEntity PersonT)
+  }
+  deriving (Generic)
+
+instance Database Postgres Db
+
+db :: DatabaseSettings Postgres Db
+db = defaultDbSettings
+
+day :: Integer -> Int -> Int -> Day
+day = fromGregorian
+
+seedRows :: [Person]
+seedRows =
+  [ Person "A" (day 2025 1 1) 1,
+    Person "B" (day 2025 1 1) 1,
+    Person "C" (day 2025 1 2) 2,
+    Person "D" (day 2025 1 2) 2,
+    Person "E" (day 2025 1 3) 3,
+    Person "F" (day 2025 1 3) 3
+  ]
+
+setupDb :: Connection -> IO ()
+setupDb conn = runBeamPostgres conn $ do
+  void $ autoMigrate migrationBackend (defaultMigratableDbSettings @Postgres @Db)
+  runInsert $ insert (persons db) $ insertValues seedRows
diff --git a/test/Database/Beam/Postgres/Test/Windowing.hs b/test/Database/Beam/Postgres/Test/Windowing.hs
new file mode 100644
--- /dev/null
+++ b/test/Database/Beam/Postgres/Test/Windowing.hs
@@ -0,0 +1,221 @@
+{-# LANGUAGE DerivingStrategies #-}
+{-# LANGUAGE NamedFieldPuns #-}
+{-# LANGUAGE StandaloneDeriving #-}
+
+module Database.Beam.Postgres.Test.Windowing (tests) where
+
+import Database.Beam
+import Database.Beam.Backend.SQL.BeamExtensions
+import Database.Beam.Migrate
+import Database.Beam.Migrate.Simple (autoMigrate)
+import Database.Beam.Postgres
+import Database.Beam.Postgres.Migrate (migrationBackend)
+import Database.Beam.Postgres.Test
+
+import Control.Exception (SomeException (..), handle)
+
+import Data.ByteString (ByteString)
+import Data.Int
+import Data.Text (Text)
+
+import Control.Monad (void)
+import Test.Tasty
+import Test.Tasty.HUnit
+
+tests :: IO ByteString -> TestTree
+tests postgresConn =
+    testGroup
+        "Windowing unit tests"
+        [ testLead1 postgresConn
+        , testLag1 postgresConn
+        , testLead postgresConn
+        , testLag postgresConn
+        , testLeadWithDefault postgresConn
+        , testLagWithDefault postgresConn
+        ]
+
+testLead1 :: IO ByteString -> TestTree
+testLead1 = testCase "lead1_" . windowingQueryTest query expectation
+  where
+    query =
+        withWindow_
+            ( \Person{name} ->
+                frame_
+                    noPartition_
+                    (orderPartitionBy_ (asc_ name))
+                    noBounds_
+            )
+            ( \Person{name} w ->
+                (name, lead1_ name `over_` w)
+            )
+            (all_ $ persons db)
+    expectation = [("Alice", Just "Bob"), ("Bob", Just "Claire"), ("Claire", Nothing)]
+
+testLag1 :: IO ByteString -> TestTree
+testLag1 = testCase "lag1_" . windowingQueryTest query expectation
+  where
+    query =
+        withWindow_
+            ( \Person{name} ->
+                frame_
+                    noPartition_
+                    (orderPartitionBy_ (asc_ name))
+                    noBounds_
+            )
+            ( \Person{name} w ->
+                (name, lag1_ name `over_` w)
+            )
+            (all_ $ persons db)
+    expectation = [("Alice", Nothing), ("Bob", Just "Alice"), ("Claire", Just "Bob")]
+
+testLead :: IO ByteString -> TestTree
+testLead getConnStr =
+    testGroup
+        "lead_"
+        [ testCase "n=1" $ windowingQueryTest (query 1) [("Alice", Just "Bob"), ("Bob", Just "Claire"), ("Claire", Nothing)] getConnStr
+        , testCase "n=2" $ windowingQueryTest (query 2) [("Alice", Just "Claire"), ("Bob", Nothing), ("Claire", Nothing)] getConnStr
+        ]
+  where
+    query n =
+        withWindow_
+            ( \Person{name} ->
+                frame_
+                    noPartition_
+                    (orderPartitionBy_ (asc_ name))
+                    noBounds_
+            )
+            ( \Person{name} w ->
+                (name, lead_ name (val_ (n :: Int32)) `over_` w)
+            )
+            (all_ $ persons db)
+    expectation1 = []
+
+testLag :: IO ByteString -> TestTree
+testLag getConnStr =
+    testGroup
+        "lag_"
+        [ testCase "n=1" $ windowingQueryTest (query 1) [("Alice", Nothing), ("Bob", Just "Alice"), ("Claire", Just "Bob")] getConnStr
+        , testCase "n=2" $ windowingQueryTest (query 2) [("Alice", Nothing), ("Bob", Nothing), ("Claire", Just "Alice")] getConnStr
+        ]
+  where
+    query n =
+        withWindow_
+            ( \Person{name} ->
+                frame_
+                    noPartition_
+                    (orderPartitionBy_ (asc_ name))
+                    noBounds_
+            )
+            ( \Person{name} w ->
+                (name, lag_ name (val_ (n :: Int32)) `over_` w)
+            )
+            (all_ $ persons db)
+    expectation = []
+
+
+testLeadWithDefault :: IO ByteString -> TestTree
+testLeadWithDefault getConnStr =
+    testGroup
+        "leadWithDefault_"
+        [ testCase "n=1" $ windowingQueryTest (query 1 "default") [("Alice", "Bob"), ("Bob", "Claire"), ("Claire", "default")] getConnStr
+        , testCase "n=2" $ windowingQueryTest (query 2 "default") [("Alice", "Claire"), ("Bob", "default"), ("Claire", "default")] getConnStr
+        ]
+  where
+    query n def =
+        withWindow_
+            ( \Person{name} ->
+                frame_
+                    noPartition_
+                    (orderPartitionBy_ (asc_ name))
+                    noBounds_
+            )
+            ( \Person{name} w ->
+                (name, leadWithDefault_ name (val_ (n :: Int32)) (val_ def) `over_` w)
+            )
+            (all_ $ persons db)
+    expectation1 = []
+
+
+testLagWithDefault :: IO ByteString -> TestTree
+testLagWithDefault getConnStr =
+    testGroup
+        "lagWithDefault_"
+        [ testCase "n=1" $ windowingQueryTest (query 1 "default") [("Alice", "default"), ("Bob", "Alice"), ("Claire", "Bob")] getConnStr
+        , testCase "n=2" $ windowingQueryTest (query 2 "default") [("Alice", "default"), ("Bob", "default"), ("Claire", "Alice")] getConnStr
+        ]
+  where
+    query n def =
+        withWindow_
+            ( \Person{name} ->
+                frame_
+                    noPartition_
+                    (orderPartitionBy_ (asc_ name))
+                    noBounds_
+            )
+            ( \Person{name} w ->
+                (name, lagWithDefault_ name (val_ (n :: Int32)) (val_ def) `over_` w)
+            )
+            (all_ $ persons db)
+    expectation = []
+
+
+
+data PersonT f = Person
+    { name :: C f Text
+    }
+    deriving (Generic)
+
+type Person = PersonT Identity
+
+type PersonExpr s = PersonT (QExpr Postgres s)
+
+deriving instance Show Person
+deriving instance Eq Person
+
+instance Beamable PersonT
+
+instance Table PersonT where
+    data PrimaryKey PersonT f = PersonKey (C f Text)
+        deriving stock (Generic)
+        deriving anyclass (Beamable)
+
+    primaryKey Person{name} = PersonKey name
+
+data Db f = Db
+    { persons :: f (TableEntity PersonT)
+    }
+    deriving (Generic)
+
+instance Database Postgres Db
+
+db :: DatabaseSettings Postgres Db
+db = defaultDbSettings
+
+windowingQueryTest ::
+    (Eq a, Show a, Eq b, Show b, FromBackendRow Postgres a, FromBackendRow Postgres b) =>
+    Q Postgres Db QBaseScope (QExpr Postgres s a, QExpr Postgres s b) ->
+    [(a, b)] ->
+    IO ByteString ->
+    Assertion
+windowingQueryTest query expectation getConnStr =
+    withTestPostgres "db_windowing_psql" getConnStr $
+        \conn -> do
+            prepareTable conn
+            results <-
+                runBeamPostgres conn $
+                    runSelectReturningList $
+                        select query
+
+            assertEqual "Unexpected" expectation results
+
+prepareTable :: Connection -> IO ()
+prepareTable conn =
+    runBeamPostgres conn $ do
+        void $ autoMigrate migrationBackend (defaultMigratableDbSettings @Postgres @Db)
+        runInsert $
+            insert (persons db) $
+                insertValues
+                    [ Person "Alice"
+                    , Person "Bob"
+                    , Person "Claire"
+                    ]
diff --git a/test/Main.hs b/test/Main.hs
--- a/test/Main.hs
+++ b/test/Main.hs
@@ -7,24 +7,30 @@
 import Test.Tasty
 import qualified TestContainers.Tasty as TC
 
-import qualified Database.Beam.Postgres.Test.Select as Select
-import qualified Database.Beam.Postgres.Test.Marshal as Marshal
+import qualified Database.Beam.Postgres.Test.Copy as Copy
 import qualified Database.Beam.Postgres.Test.DataTypes as DataType
+import qualified Database.Beam.Postgres.Test.Marshal as Marshal
 import qualified Database.Beam.Postgres.Test.Migrate as Migrate
+import qualified Database.Beam.Postgres.Test.Select as Select
+import qualified Database.Beam.Postgres.Test.Select.PgNubBy as Select.PgNubBy
 import qualified Database.Beam.Postgres.Test.TempTable as TempTable
+import qualified Database.Beam.Postgres.Test.Windowing as Windowing
 import Database.PostgreSQL.Simple ( ConnectInfo(..), defaultConnectInfo )
 import qualified Database.PostgreSQL.Simple as Postgres
 
 main :: IO ()
-main = defaultMain 
-     $ TC.withContainers setupTempPostgresDB 
-     $ \getConnStr -> 
+main = defaultMain
+     $ TC.withContainers setupTempPostgresDB
+     $ \getConnStr ->
         testGroup "beam-postgres tests"
           [ Marshal.tests getConnStr
           , Select.tests getConnStr
+          , Select.PgNubBy.tests getConnStr
           , DataType.tests getConnStr
           , Migrate.tests getConnStr
           , TempTable.tests getConnStr
+          , Windowing.tests getConnStr
+          , Copy.tests getConnStr
           ]
 
 
@@ -41,10 +47,10 @@
                        , ("POSTGRES_DB", db)
                        ]
         TC.& TC.setWaitingFor (TC.waitForLogLine TC.Stderr ("database system is ready to accept connections" `TL.isInfixOf`))
-    
-    pure $ Postgres.postgreSQLConnectionString 
+
+    pure $ Postgres.postgreSQLConnectionString
                    ( defaultConnectInfo { connectHost     = "localhost"
-                                        , connectUser     = unpack user 
+                                        , connectUser     = unpack user
                                         , connectPassword = unpack password
                                         , connectDatabase = unpack db
                                         , connectPort     = fromIntegral $ TC.containerPort timescaleContainer 5432
