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--- name: motherduck-query description: Execute DuckDB SQL queries against MotherDuck databases. Use when running analytics, aggregations, transformations, or any SQL operation. Covers query best practices, CTEs, window functions, QUALIFY, and performance optimization. license: MIT --- # Query MotherDuck Use this skill when executing SQL queries for analytics, aggregations, transformations, or data exploration against MotherDuck databases. ## Prerequisites - An established MotherDuck connection (or an active MotherDuck MCP server) - Target database and tables identified ## Default Posture - When MotherDuck MCP is available and the query answers a business question, call `get_query_guide` before writing SQL. Traverse only relevant topics and validate Guide claims against the live schema. - Write DuckDB SQL, not PostgreSQL SQL, even when using the PG endpoint. - Always use fully qualified `"database"."schema"."table"` names. - Preserve the intended grain of every result set; state the grain before optimizing or materializing a query. - Filter early, aggregate early, and prefer serving tables or summaries for repeated reads. - Keep SQL obvious, multi-line, and explicit about grain, filters, and output shape. - Treat DDL, DML, `ATTACH`, `DETACH`, recovery commands such as `CREATE SNAPSHOT`, `ALTER DATABASE ... SET SNAPSHOT`, `UNDROP DATABASE`, and lifecycle commands such as `SHUTDOWN` as writes. Use the MotherDuck MCP `query_rw` tool when the user's change request authorizes the write. Ask for confirmation only when the action is destructive, externally visible, or outside the stated scope. - Tag long-lived integrations with `custom_user_agent` when the connection path supports it. ## Workflow 1. Confirm the actual tables, columns, and grain before writing SQL. 2. Load relevant Guide context when MCP is available, without treating it as a substitute for schema inspection. 3. Write the query in SQL first, then wrap it in Python or TypeScript only if needed. 4. Use CTEs and DuckDB-native patterns such as `GROUP BY ALL`, `QUALIFY`, and `arg_max`. 5. Check the plan, row count, and shape for pushdown, unnecessary sorts, or repeated raw rescans. 6. Materialize expensive repeated queries into serving tables or light views when warranted. ## Open Next - Read `references/QUERY_PLAYBOOK.md` for DuckDB query patterns, exploration SQL, performance rules, common analytical shapes, and common mistakes ## Related Skills - `motherduck-connect` for session setup - `motherduck-duckdb-sql` for syntax and function reference - `motherduck-explore` for understanding the source schema before writing queries - `motherduck-manage-guides` when semantic definitions or reusable query rules need to be read or maintained