#moonduckdb

moon add moonbitstack/moonduckdb

let db = @moonduckdb.DuckdbDriver::open(":memory:")
db.exec_script("CREATE TABLE hero (id INTEGER PRIMARY KEY, name VARCHAR)")
db.execute("INSERT INTO hero VALUES (?, ?)", [Int(1), Text("Nova")]) |> ignore
let rows = db.query("SELECT name FROM hero WHERE id = ?", [Int(1)])
println(rows[0].text_by("name")) // Nova

#The engine is loaded, not compiled

drivers/duckdb/scripts/fetch_engine.sh    # downloads the pinned release for this platform
# → drivers/duckdb/engine/linux-amd64/libduckdb.so

MOONDUCKDB_LIBRARY=/path/to/libduckdb.so moon test --target native

#The same driver on the js target

drivers/duckdb/scripts/fetch_wasm_engine.sh   # npm-installs the pinned build
export MOONDUCKDB_ENGINE=$(drivers/duckdb/scripts/fetch_wasm_engine.sh)

async fn demo() -> Unit raise @moondb.DbError {
  let db = @moonduckdb.DuckdbDriver::open(":memory:")
  db.execute("CREATE TABLE t (id INTEGER, n VARCHAR)", []) |> ignore
  db.execute("INSERT INTO t VALUES (?, ?)", [Int(1), Text("a")]) |> ignore
  let rows = db.query("SELECT n FROM t", [])
  println(rows[0].text(0))   // a
  db.close()
}

• A 64-bit parameter crosses as a Number, because the worker protocol is JSON and JSON has no BigInt. A value above 2⁵³ loses its low bits on this target; native carries all 64.
• A blob parameter travels as \xNN escapes, DuckDB's own STRING-to-BLOB form, for the same reason: a typed array does not survive the JSON hop, and the escapes land unchanged.
• One database per module instance. Opening a connection re-opens the database, so two :memory: databases are isolated from each other, but two connections open at once see one catalog.

#What it adds to the contract

• A dialect of its own. Dialect::Duckdb: ? placeholders like SQLite, PostgreSQL's type names (VARCHAR, DOUBLE, BLOB) and its own (HUGEINT, UBIGINT). A query layer that emitted SQLite's REAL or PostgreSQL's $1 would be wrong here.
• Transactions, but no savepoints. begin/commit/rollback are real; SAVEPOINT is not implemented, so capabilities().savepoints is false and the conformance matrix records the nested-bracket case as skipped with that reason.
• Prepared statements are real. prepare sends DuckDB's PREPARE, and a repeated insert binds new values to the same plan.

#Type mapping

#Tested against a real engine

#Not covered

• Array parameters. The C API this driver uses binds scalars; pass an array as its text literal ([1, 2, 3]) instead, and read array columns back as text.
• The appender and bulk COPY. A large load belongs in DuckDB's own COPY … FROM statement, run through exec_script.
• Windows path handling in the loader. MOONDUCKDB_LIBRARY takes a plain path; a space in it is fine, a UNC path was not tested.

#License