Four categories:
-Queries using the SELECT command.
-Statements using the CREATE, ALTER, or DROP command are classified as Data Definition Language (DDL) commands.
-Statements using the GRANT or REVOKE commands are classified as Data Control Language(DCL) commands.
-Statements using the INSERT, UPDATE, and DELETE commands are classified as Data Manipulation Language (DML) commands.
Transactions: DML commands are used in transactions. A transaction begins with the first DML command that a user issues and ends when the user either makes their changes permanent by issuing a commit command or undoes their changes using the rollback command.
