DQL, DDL, DML, DCL introduce the concept, not too much specific examples demonstrate:
DQL: database query language. Keywords: SELECT ... FROM ... WHERE.
DDL: database schema definition language. Keywords: CREATE, DROP, ALTER.
DML: Data Manipulation Language. Keywords: INSERT, UPDATE, DELETE.
DCL: Data Control Language. Keywords: GRANT, REVOKE.
TCL: Transaction Control Language. Keywords: COMMIT, ROLLBACK, SAVEPOINT.
DDL, DML, DCL, DQL, TCL together to form a complete language database.
