SQL stands for Structured Query Language is a built-in language for querying a database. With SQL, you can change the data you have in your database the way you want it to be retrieved if you want it to.
To practice with SQL you need a database such as SQL – server and Access or Oracle or any other database.
Although SQL is a language under the ANSI (American National Standards Institute) standard, each database uses its own version, so some commands in one database may be based on a version of SQL that uses commands in another database. A little different.
The SQL language commands are divided into five categories:
- DDL (Data Definition Language) Data Definition Language.
- DML (Data Manipulation Language) Data processing language.
- DCL (Data Control Language) Commands for data management and control.
- DQL (Data Query Language) data query commands.
- Transaction control commands.
- Data management commands.
In the first category, DDL is the language that can create or delete a database table. The commands in this category are as follows:
CREATE, ALTER, DROP, CREATE INDEX, ALTER INDEX, DROP INDEX
The second category is DML commands , which are used to make changes to tables that consist of three main commands:
INSERT, UPDATE, DELETE
The third category is DQL commands , which consist of only one command, called SELECT, which encompasses the maximum amount of workload for a SQL user. This command, along with several commands that exist within it, is due to the widespread use of this command.
The fourth category is DCL . As the name implies, it is used to control database data that is more about accessing this data to other users. Which consists of the following commands:
ALTER PASSWORD, REVOKE, GRANT, CREATE SYNONYM
The next category is the TRANSACTION control commands that allow the user to manage the database transaction. That consist of the following commands:
COMMIT, ROLLBACK, SAVEPOINT, SET TRANSACTION
And the last batch that complemented the earlier batch commands are data management commands that allow analysis and analysis of operations within the database. Also remember not to confuse this with database management.