SQL commands are instructions, coded into SQL statements, which are used to communicate with the database to perform specific tasks, work, functions and queries with data.
SQL commands can be used not only for searching the database but also to perform various other functions like, for example, you can create tables, add data to tables, or modify data, drop the table, set permissions for users. SQL commands are grouped into four major categories depending on their functionality:
Data Definition Language (DDL) - These SQL commands are used for creating, modifying, and dropping the structure of database objects. The commands are CREATE, ALTER, DROP, RENAME, and TRUNCATE.
Data Manipulation Language (DML) - These commands are used for storing, retrieving, modifying, and deleting data. These Data Manipulation Language commands are: SELECT, INSERT, UPDATE, and DELETE.
Transaction Control Language (TCL) - These SQL commands are used for managing changes affecting the data.
These commands are COMMIT, ROLLBACK, and SAVEPOINT.
Data Control Language (DCL) - These SQL commands are used for providing security to database objects.
These commands are GRANT and REVOKE.