Sql Commands - (DDL (Data Definition Language), DML (Data Manipulation Language), DCL (Data Control Language), TCL (Transaction Control Language)

SQL language is divided into four types of primary language statements: DML, DDL, DCL, and TCL. Using these statements, we can define the structure of a database by creating and altering database objects, and we can manipulate data in a table through updates or deletions. We also can control which user can read/write data or manage transactions to create a single unit of work.

The four main categories of SQL statements are as follows:

1. DDL (Data Definition Language)
2. DML (Data Manipulation Language)
3. DCL (Data Control Language)
4. TCL (Transaction Control Language)

DDL -Data Definition Language:

DDL (DataDefinition Language) command is used for defining the structure of the Data. DDL Statements are auto-commit.

CREATE                   -      to create objects in the database

ALTER                      -     alters the structure of the database

DROP                        -     delete objects from the database

TRUNCATE              -     remove all records from a table, including all spaces

                                         allocated for the records are removed

COMMENT              -     add comments to the data dictionary

RENAME                  -     rename an object

DML - Data Manipulation Language:

DML (data manipulation Language) statements are used for managing

data within schema objects.

• DML Statements can be rollbacked.
• DML Statements can’t be roll backed When DDL Statement Executed immediately after the DML statement.

Command	Description
INSERT                         -	Insert data into a table.
UPDATE                        -	Updates existing data within a table.
DELETE                        -	Deletes all records from a table, the space for the records remain

 DQL - Data Query Language:

Command	Description
SELECT                         -	Retrieves certain records from one or more tables.

DCL - Data Control Language:

Command	Description
GRANT                           -	Gives user's access privileges to a database.
REVOKE                        -	Withdraw access privileges given with the GRANT command.

TCL - (Transaction Control Language) 

 (Transaction Control Language) Manages the changes made by DML statements. These commands allow statements to be grouped together into logical transactions.

Command

Description

COMMIT           -    Save work done.

SAVEPOINT      -    Identify a point in a transaction to which you can later roll back.

ROLLBACK      -    Restore database to original since the last COMMIT.