The SQL commands are divided into the following groups:
- DDL – Data Definition Language
- DML – Data Manipulation Language
- DQL – Data Query Language
- DCL – Data Control Language
- TCL – Transaction Control Language
Let’s take a closer look at each of them.
DDL
- This category includes queries like CREATE, DROP, TRUNCATE, and ALTER since they all manage the structure of DB Objects in some way.
- For example, the CREATE command constructs the structure of a table, but the DROP command deletes the table structure.
DML
- This category includes queries like DELETE, UPDATE, and INSERT since they all alter data in some way.
- For example, the DELETE command deletes data from a table, but the UPDATE command modifies the data.
DQL
- This category includes the SELECT query, used to query the database and obtain the query’s result.
- For example, we may use SELECT to ask a database any specified question and retrieve replies.
DCL
- GRANT and REVOKE queries come under this category since they are used to control access to the database.
- Provide, for example, will grant permission to a user on a DB Object, whereas REVOKE will revoke the access.
TCL
- Queries like ROLLBACK, COMMIT and SAVE POINT come under this category since they are used to control database transactions.
- For example, when a transaction fails, the COMMIT command commits the transaction, and the ROLLBACK command rolls back all changes made to the database.
