What are the major categories of SQL commands?

SQL commands are commonly grouped conceptually into DDL, DML, DQL, DCL, and TCL.

DDL defines database structures, such as CREATE, ALTER, and DROP. DML modifies data, such as INSERT, UPDATE, and DELETE. DQL retrieves data, primarily with SELECT. DCL manages permissions using commands such as GRANT, DENY, and REVOKE. TCL manages transactions using BEGIN TRANSACTION, COMMIT, and ROLLBACK.

The exact classification terminology can vary between books and interviewers, but these categories are useful for explaining the purpose of SQL statements.