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Provides SQL optimization patterns for query performance, indexing strategies, schema design, and database tuning. Use when optimizing slow queries, designing indexes, or tuning database performance.
| name | sql-optimization-patterns |
| type | reference |
| description | Provides SQL optimization patterns for query performance, indexing strategies, schema design, and database tuning. Use when optimizing slow queries, designing indexes, or tuning database performance. |
| paths | ["**/*.sql","**/migrations/**"] |
| effort | 3 |
| allowed-tools | Read, Glob, Grep, Bash |
| user-invocable | true |
| when_to_use | When optimizing slow SQL queries, designing indexes, or tuning database performance |
Query optimization, indexing, and performance tuning for PostgreSQL, MySQL, and SQLite.
```sql -- High selectivity columns (many unique values) CREATE INDEX idx_orders_user_id ON orders(user_id);
-- Composite index: order matters (equality first, then range) CREATE INDEX idx_orders_user_date ON orders(user_id, created_at DESC);
-- Covering index (includes all needed columns) CREATE INDEX idx_orders_covering ON orders(user_id, status) INCLUDE (total, created_at); ```
```sql -- Bad SELECT * FROM orders WHERE user_id = 1;
-- Good (select only needed columns) SELECT id, total, status FROM orders WHERE user_id = 1; ```
```sql -- Bad: N+1 queries from application -- Good: Single query with JOIN SELECT o.id, o.total, u.name FROM orders o JOIN users u ON o.user_id = u.id WHERE o.status = 'pending'; ```
```sql -- Bad: OFFSET scans all skipped rows SELECT * FROM orders ORDER BY id LIMIT 20 OFFSET 10000;
-- Good: Keyset pagination SELECT * FROM orders WHERE id > 10000 ORDER BY id LIMIT 20; ```
```sql EXPLAIN ANALYZE SELECT * FROM orders WHERE user_id = 1 AND status = 'pending'; ```
Read output:
| Anti-Pattern | Problem | Fix |
|---|---|---|
| EAV (Entity-Attribute-Value) | No type safety, slow queries | Use JSONB or proper columns |
| God table | Too many columns | Normalize into related tables |
| No constraints | Data integrity issues | Add CHECK, FK, UNIQUE constraints |
| String dates | Sorting/filtering issues | Use TIMESTAMP type |
``` App → Pool (min: 5, max: 20) → PostgreSQL ```
Tools: PgBouncer (PostgreSQL), ProxySQL (MySQL).
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