Individual skill
sql
Use when writing or reviewing advanced SQL query logic independent of any one engine — multi-table joins, window functions, CTEs including recursive ones, GROUP BY and GROUPING SETS aggregation, and set operations — or when a query returns too many rows, too few, or wrong totals. NOT engine internals, indexes or EXPLAIN (that is `postgresdb`), NOT MySQL config (that is `mysql`), NOT OLAP columnar specifics (that is `duckdb`).
skills/sql/SKILL.md
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- Last checked
- Nov 6, 2026
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- 562
- Repository last updated
- Nov 4, 2026
- License
- MIT
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- sql Declared skill tag
- query Declared skill tag
- joins Declared skill tag
- window-functions Declared skill tag
- cte Declared skill tag
- data Derived category
- operations Derived category
- writing Derived category
- data-databases Derived category
Files and excerpt
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Browse files
SKILL.mdcore · 15,214 bytesSKILL.mdcore · 15,214 bytesevals/README.mddoc · 1,473 bytesevals/cases.yamlasset · 3,116 bytesreferences/ctes-and-recursion.mddoc · 2,807 bytesreferences/joins-and-sets.mddoc · 3,304 bytesreferences/portability.mddoc · 2,879 bytesreferences/window-functions.mddoc · 3,754 bytesscripts/verify.shruns · 5,632 bytes
Read excerpt
# SQL — engine-agnostic query craft
This skill is the portable query-writing layer that sits *above* any one database engine. It owns
the SELECT-side craft: joins and what each does to row count and NULLs, window functions
(`PARTITION`/`ORDER`/frame), CTEs (including recursive), aggregation (`GROUP BY`/`GROUPING SETS`/`HAVING`),
set operations (`UNION`/`INTERSECT`/`EXCEPT`), conditional logic (`CASE`/`COALESCE`/`NULLIF`), and the
NULL three-valued-logic traps that quietly corrupt results across *every* engine. You write queries a
reviewer accepts on Postgres, MySQL 8, SQLite, DuckDB, SQL Server, or BigQuery with minimal change, and
you flag exactly where a construct is non-portable and what the dialect substitute is. The target
standard is **SQL:2023 (ISO/IEC 9075:2023)**, the ninth edition published June 2023; window functions
have been standard since **SQL:2003**, so they are safe to assume everywhere.
This is about *thinking in sets and frames*, not about one product's planner, DDL, indexing, or ops.
