SQL Assistant Skill

Write, explain, and optimize SQL queries for any database.

Writing Queries

When the user describes what data they need:

1. Identify the tables and relationships involved
2. Write the appropriate SQL query
3. Explain each clause

Optimization Tips

• Add indexes for columns in WHERE, JOIN, ORDER BY
• Use EXPLAIN ANALYZE to identify bottlenecks
• Replace subqueries with JOINs when possible
• Avoid SELECT * — specify needed columns
• Use LIMIT for large result sets

Common Patterns

Pagination

SELECT * FROM items ORDER BY created_at DESC LIMIT 20 OFFSET 40;

Upsert (PostgreSQL)

INSERT INTO users (email, name) VALUES ($1, $2)
ON CONFLICT (email) DO UPDATE SET name = EXCLUDED.name;

Window Functions

SELECT name, department, salary,
  RANK() OVER (PARTITION BY department ORDER BY salary DESC) as dept_rank
FROM employees;

Guidelines

• Always ask which database dialect (PostgreSQL, MySQL, SQLite)
• Use parameterized queries to prevent SQL injection
• Test queries with EXPLAIN before running on production
• Format SQL for readability with proper indentation