DuckDB MSSQL Extension

Connect DuckDB to Microsoft SQL Server, Azure SQL and Microsoft Fabric over a native TDS 7.4 implementation — no ODBC, no JDBC, no FreeTDS. Attach a database and it becomes a DuckDB catalog: stream reads with filter and ORDER BY pushdown, bulk-load writes over the BCP protocol at millions of rows per second, full DML and transactions.

INSTALL mssql FROM community;
LOAD mssql;

ATTACH 'Server=localhost;Database=AdventureWorks;User Id=sa;Password=...' AS mssql (TYPE mssql);
SELECT * FROM mssql.dbo.SalesOrderHeader LIMIT 10;

→ Getting Started · Settings Reference · Download metrics

Community Extension Downloads

📊 Interactive chart — queried live in your browser with DuckDB-Wasm. Regenerated weekly; counts are a Cloudflare estimate of INSTALL mssql FROM community events across DuckDB versions and platforms.

Features

• Native TDS protocol implementation (no external dependencies)
• Stream query results directly into DuckDB without buffering
• Full DuckDB catalog integration with three-part naming and lazy metadata loading
• Row identity (rowid) support for tables with primary keys
• Connection pooling with configurable limits and automatic session reset
• TLS/SSL encrypted connections
• Full DML support: INSERT (with RETURNING), UPDATE, DELETE
• CREATE TABLE AS SELECT (CTAS) with streaming and type mapping
• High-performance COPY TO via TDS BulkLoadBCP protocol
• Transaction support: BEGIN/COMMIT/ROLLBACK with connection pinning
• Multi-statement SQL batches via mssql_scan() (e.g., temp table workflows)
• DuckDB secret management for secure credential storage
• Azure AD authentication (service principal, CLI, interactive device code flow)
• Kerberos / Windows SSPI integrated authentication — POSIX (kinit / keytab / raw credentials) and Windows (current logon session via secur32.dll)
• Custom Application Name propagated to SQL Server APP_NAME() / sys.dm_exec_sessions.program_name
• ATTACH-time credential validation (opt-out via lazy_validation true)
• Experimental: ORDER BY pushdown to SQL Server (opt-in via mssql_order_pushdown setting)

Platform Support

Platform	Status	Notes
macOS ARM64	Primary development	Active development and testing
Linux x86_64	CI-validated	Automated builds and tests in CI
Linux ARM64	CI-validated	Automated builds and tests in CI
Windows x64	CI-validated	Automated builds and tests in CI

Roadmap

Current release: v0.2.3 — the performance series. Reads stage column-major with batch decode (−14…−47% per family), writes encode column-major over parallel bulk-load sessions (up to 6.6×), UTF-8 end to end, declared string types for table creation. Details in the release notes.

v0.3.0 — DML pushdown and federation (reconnaissance complete, specs in progress):

Feature	What it does	Status
Direct UPDATE/DELETE	When the whole WHERE pushes down, emit one UPDATE/DELETE ... WHERE statement — no scan, no rowid round trip. Also lifts the primary-key requirement for pushable statements (#140)	Spec drafted
INSERT over BCP	INSERT INTO ... SELECT switches from batched VALUES text to the bulk-load protocol (2–10×)	Spec drafted
UPDATE/DELETE via staging	Affected rows bulk-load into a session #temp, one server-side UPDATE ... JOIN #stage replaces per-batch VALUES joins	Spec drafted
MERGE INTO + upsert	MERGE INTO planning (DuckDB lowers INSERT ... ON CONFLICT to MERGE, so both arrive together); full T-SQL MERGE pushdown for same-catalog sources	Recon complete
Same-catalog read-then-write in transactions	Materialize the extension's own scans before a bulk-load sink starts (the duckdb-postgres pattern), removing a documented limitation (#239)	Recon complete
JOIN / aggregate pushdown	Semi-join reduction (always-safe), shipping small local tables to the server via BCP for server-side joins, and pushed GROUP BY / aggregates with exact type mapping	Recon complete
ORDER BY pushdown by default	Collation-aware safety predicate; native server semantics as the default contract	Spec drafted

Under consideration

Topic	What we're thinking about
VARIANT fallback	UDT / SQL_VARIANT columns as DuckDB VARIANT instead of today's NVARCHAR(MAX) auto-CAST text form. Opt-in via a setting.
TRUNCATE optimization	Auto-detect DELETE FROM t without WHERE and emit TRUNCATE TABLE when safe (no triggers/FK/CCI).
DuckLake metadata backend	SQL Server as a DuckLake catalog store (#129).

Support MSSQL Extension

MSSQL Extension is an open-source DuckDB extension maintained in spare time.

If it helps you or your organization, consider sponsoring its development through GitHub Sponsors.

Your support helps fund maintenance, bug fixes, testing, and new features.