duckdb-haskell
Full-featured Haskell bindings for DuckDB.
Installation
The library is available on Hackage.
Usage
Database.DuckDB.Internal.FFI: fully FFI bindings to the DuckDB C API
Database.DuckDB.Connection: connection management
Database.DuckDB.Query: query execution
Database.DuckDB.Appender: bulk data loading
Connection
Query results
-
Query from the database:
query42Test :: TestTree
query42Test = testCase "Query the constant (42)" $ do
r <- runDuckDB $ withDefaultConnection $ \(_db, conn) -> do
r <- query conn "select 42;"
v <- valueInt32 r 0 0
liftIO $ v @?= 42
r @?= Right ()
-
Query from the database, more complex example:
queryCreateTableTest :: TestTree
queryCreateTableTest = testCase "Create table and query" $ do
r <- runDuckDB $ withDefaultConnection $ \(_db, conn) -> do
_ <- query conn "CREATE TABLE integers (i INTEGER)"
_ <- query conn "INSERT INTO integers VALUES (1), (2), (3), (999)"
r <- query conn "SELECT i FROM integers"
valueInt32 r 0 0 >>= \v -> liftIO $ v @?= 1
valueInt32 r 0 1 >>= \v -> liftIO $ v @?= 2
valueInt32 r 0 2 >>= \v -> liftIO $ v @?= 3
valueInt32 r 0 3 >>= \v -> liftIO $ v @?= 999
r @?= Right ()
-
Query from the database, inspecting the value using Data.Vector.Storable:
queryDataVector :: TestTree
queryDataVector = testCase "Create table and query as efficient vectors" $ do
r <- runDuckDB $ withDefaultConnection $ \(_db, conn) -> do
_ <- query conn "CREATE TABLE integers (i INTEGER)"
_ <- query conn "INSERT INTO integers VALUES (1), (2), (3), (999)"
r <- query conn "SELECT i FROM integers"
nchk <- chunkCount r
liftIO $ nchk @?= 1
chk <- chunkAt r 0
columns <- getChunkColumnCount chk
liftIO $ columns @?= 1
rows <- getChunkSize chk
liftIO $ rows @?= 4
pointer <- getVectorData =<< getChunkVector chk 0
liftIO $ do
vec <-
Vec.unsafeFromForeignPtr0 <$> newForeignPtr_ pointer <*> (pure rows)
:: IO (Vec.Vector Int32)
vec @?= Vec.fromList [1, 2, 3, 999]
r @?= Right ()
Bulk data loading
-
Efficiently loading data using appenders:
appenderTableTest :: TestTree
appenderTableTest = testCase "Create table, append data and query" $ do
r <- runDuckDB $ withDefaultConnection $ \(_db, conn) -> do
_ <- query conn "CREATE TABLE integers (i INTEGER, j INTEGER)"
withAppender conn "" "integers" $ \app ->
forM_ [1 .. 100] $ \i -> withAppenderRow app $ do
appendInt32 app i
appendInt32 app (i + 99)
r <- query conn "SELECT i, j FROM integers"
liftIO $ chunkCount r >>= print