Database

Database

Database operations, queries, migrations, and optimization.

Supported Databases

Basic Operations

PostgreSQL

# Connect
psql -h localhost -U username -d database

# Run query
psql -c "SELECT * FROM users LIMIT 10;"

# Execute file
psql -f migration.sql

SQLite

# Create/​open database
sqlite3 data.db

# Run query
sqlite3 data.db "SELECT * FROM logs;"

Common Tasks

1. Schema Inspection

-- PostgreSQL: List tables
\dt

-- SQLite: List tables
.tables

-- MySQL: List tables
SHOW TABLES;

2. Backup/​Restore

# PostgreSQL backup
pg_dump -h localhost -U user dbname > backup.sql

# PostgreSQL restore
psql -h localhost -U user dbname < backup.sql

# SQLite backup
sqlite3 source.db ".backup backup.db"

3. Migration Pattern

migrations/
  001_create_users.sql
  002_add_email_index.sql
  003_create_orders.sql

Run in order:

for f in migrations/​*.sql; do
  psql -f "$f"
done

Query Optimization

Check Slow Queries (PostgreSQL)

SELECT query, mean_time, calls 
FROM pg_stat_statements 
ORDER BY mean_time DESC 
LIMIT 10;

Add Index

CREATE INDEX CONCURRENTLY idx_users_email ON users(email);

Best Practices

1. Use connection pooling — Don't open connections per query
2. Parameterized queries — Prevent SQL injection
3. Index foreign keys — Automatic in most DBs, verify
4. Regular backups — Automate with cron
5. Monitor slow queries — Catch performance issues early
6. Migrations — Version control your schema

Security

• Never commit credentials
• Use .env files for connection strings
• Restrict database user permissions
• Enable SSL for remote connections