Postgresql

PostgreSQL 16+ Reference

Version: 16+. All syntax is standard; most features apply to PostgreSQL 13+.

Quick patterns

-- Check running queries
SELECT pid, state, wait_event_type, query FROM pg_stat_activity WHERE state != 'idle';

-- Explain a slow query
EXPLAIN (ANALYZE, BUFFERS, FORMAT TEXT) SELECT ...;

-- List table sizes
SELECT relname, pg_size_pretty(pg_total_relation_size(oid)) FROM pg_class
WHERE relkind = 'r' ORDER BY pg_total_relation_size(oid) DESC;

-- Kill a blocking query
SELECT pg_terminate_backend(pid) FROM pg_stat_activity WHERE pid = <pid>;

Key non-obvious facts

• Every statement runs in a transaction. Without BEGIN, each statement auto-commits.
• jsonb stores parsed binary (faster queries); json stores raw text (exact input preserved). Prefer jsonb.
• LIKE 'foo%' can use B-tree; LIKE '%foo' cannot — use pg_trgm GIN for suffix search.
• CREATE INDEX CONCURRENTLY avoids table lock but cannot run inside a transaction block.
• EXPLAIN without ANALYZE shows the planner's estimate. Always use EXPLAIN (ANALYZE, BUFFERS) for real data.
• Null values are stored in indexes by B-tree (unlike some other databases). IS NULL can use an index.
• SERIAL/BIGSERIAL are shorthand for sequence + default; prefer GENERATED ALWAYS AS IDENTITY (SQL standard).
• Default isolation level is Read Committed. SERIALIZABLE prevents all anomalies but may abort transactions.

Reference files

Load the relevant file when working on a specific topic: