query-rewriter

name	query-rewriter
description	SQL query rewriting expert. Identifies inefficient query patterns and provides optimized alternatives. Trigger when user mentions query optimization, SQL rewriting, or query performance.
when_to_use	- User has slow SQL queries - User needs to optimize database performance - User encounters N+1 query problems - User wants to rewrite inefficient queries - User needs to reduce database costs
allowed-tools	Bash(psql *, wrangler *)

SQL Query Rewriting Expert

Common Anti-Patterns

Anti-Pattern	Problem	Reference
SELECT *	Fetches unnecessary data	references/select-star.md
N+1 queries	Too many round trips	references/n-plus-one.md
IN with subquery	May process too many rows	references/exists-vs-in.md
OR across columns	Prevents index usage	references/or-optimization.md
OR conditions	Cannot use index	references/union-instead-of-or.md
Type mismatch	Implicit conversion	references/implicit-conversion.md

Audit Workflow

Step 1: Identify Problem Patterns

Check for:

• SELECT * usage
• N+1 query patterns
• IN with large subqueries
• OR conditions across columns
• Type mismatches

Step 2: Match Anti-Pattern

Identify which anti-pattern the query matches and apply the corresponding solution from the reference file.

Step 3: Apply Rewrite

Follow the specific reference file for detailed instructions.

Step 4: Verify Improvement

EXPLAIN ANALYZE <rewritten_query>;

Benchmark Reference

Optimization	Before	After	Improvement
SELECT * → specific	100ms	20ms	80%
N+1 → batch	500ms	50ms	90%
IN → EXISTS	500ms	50ms	90%
OR → UNION	200ms	20ms	90%
Type fix	150ms	2ms	98.7%

Output Format

## Query Rewriting Report

### 1. Original Query
```sql
<original_query>

2. Anti-Patterns Detected

Pattern	Problem	Reference
...	...	...

3. Recommended Rewrite

<optimized_query>

4. Expected Improvement

• Query time: Xms → Yms (Z% faster)
• Rows processed: X → Y (Z% reduction)

5. Implementation

Reference: references/.md