Database Specialist

Expert in database engineering, focusing on PostgreSQL, data modeling, complex SQL queries, and performance optimization.

When to Use This Skill

• Designing database schemas (ERD)
• Writing complex SQL queries (CTEs, Window Functions)
• Optimizing slow queries (EXPLAIN ANALYZE)
• Managing database migrations
• Implementing advanced data patterns (Recursive queries, JSONB)

Core Competencies

1. Advanced SQL Methodology

CTEs (Common Table Expressions) Use for readability over nested subqueries.

WITH regional_sales AS (
    SELECT region, SUM(amount) as total_sales
    FROM orders
    GROUP BY region
), top_regions AS (
    SELECT region
    FROM regional_sales
    WHERE total_sales > (SELECT AVG(total_sales) FROM regional_sales)
)
SELECT * FROM top_regions;

Window Functions Use for analytics across rows.

SELECT
    product_name,
    group_name,
    price,
    RANK() OVER (PARTITION BY group_name ORDER BY price DESC)
FROM products;

2. Performance & Indexing

The Indexing Strategy

1. B-Tree: Default. Good for =, inequalities, and sorting.
2. GIN: For JSONB and Full-Text Search.
3. GiST: For Geometric data and Range types.
4. Partial Index: CREATE INDEX ... WHERE active = true; (Saves space).

Query Analysis Always check EXPLAIN (ANALYZE, BUFFERS).

• Seq Scan: Bad for large tables.
• Index Scan: Good.
• Bitmap Heap Scan: Good for combining multiple indexes.

3. Data Integrity

• Foreign Keys: Always enforce relationships.
• Constraints: CHECK (price > 0), UNIQUE (email).
• Transactions: Use BEGIN; ... COMMIT; for atomic operations.
  • Isolation Levels: Understand READ COMMITTED vs SERIALIZABLE.

Best Practices

• Never store logic in DB: Keep business logic in app code (mostly), unless it's strictly data validation.
• Migrations: Always use versioned migrations (e.g., Prisma, Flyway).
• Normalize execution: Don't N+1. Batch queries or use joins.

Resources

• Use The Index, Luke
• PostgreSQL Documentation