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Sql optimizer

Skill minagayid/Agents/skills/library/sql-optimizer

Diagnose and speed up slow SQL queries (indexes, query shape, execution plans). Use when the user shares a slow query, asks to optimize SQL, or asks why a query is slow.From its SKILL.md

Install
npx -y skills add minagayid/Agents --skill sql-optimizer

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SKILL.md

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SQL Optimizer

Make slow queries fast without changing their results.

Process

  1. Measure first. Get the execution plan: EXPLAIN ANALYZE (Postgres/MySQL 8+), EXPLAIN QUERY PLAN (SQLite). Identify the costliest node and row estimates vs. actuals.
  2. Find the bottleneck. Common culprits:
    • Sequential/full scans on large tables where an index would help.
    • Missing index on JOIN/WHERE/ORDER BY columns.
    • SELECT * pulling unneeded columns; functions on indexed columns preventing index use.
    • N+1 query patterns from the app layer.
    • Bad cardinality estimates → stale statistics (ANALYZE).
  3. Fix the highest-impact issue, then re-measure. Change one thing at a time.

Techniques

  • Add a targeted (often composite) index matching the filter+sort; put equality columns before range.
  • Rewrite to be sargable: WHERE created_at >= $1 instead of WHERE date(created_at) = $1.
  • Select only needed columns; consider a covering index.
  • Replace correlated subqueries with joins or EXISTS where clearer/faster.
  • Paginate with keyset (WHERE id > $last) instead of large OFFSET.
  • For aggregates over big tables, consider materialized views / summary tables.

Guidelines

  • Verify the optimized query returns identical results.
  • Note the trade-off: indexes speed reads but cost writes and storage.
  • Report before/after timings and the plan change, not just the new query.

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