What is SQL and what are its main categories of statements?

SQL (Structured Query Language) is the standard language for interacting with relational databases. It is divided into: DDL (Data Definition Language) — defines schema: CREATE, ALTER, DROP, TRUNCATE; DML (Data Manipulation Language) — manipulates data: SELECT, INSERT, UPDATE, DELETE; DCL (Data Control Language) — controls access: GRANT, REVOKE; TCL (Transaction Control Language) — manages transactions: COMMIT, ROLLBACK, SAVEPOINT. SQL is declarative — you describe what data you want, not how to retrieve it; the query planner figures out the execution plan.