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What Is Structure Query Language(SQL) ?

Introduction to SQL

Structure Query Language(SQL) is a programming language used for storing and managing data in RDBMS. SQL was the first commercial language introduced for E.F Codd’s Relational model. Today almost all RDBMS(MySql, Oracle, Infomix, Sybase, MS Access) uses SQL as the standard database language. SQL is used to perform all type of data operations in RDBMS.


SQL Command

SQL defines following data languages to manipulate data of RDBMS.


DDL : Data Definition Language

All DDL commands are auto-committed. That means it saves all the changes permanently in the database.

Command Description
create to create new table or database
alter for alteration
truncate delete data from table
drop to drop a table
rename to rename a table

DML : Data Manipulation Language

DML commands are not auto-committed. It means changes are not permanent to database, they can be rolled back.

Command Description
insert to insert a new row
update to update existing row
delete to delete a row
merge merging two rows or two tables

TCL : Transaction Control Language

These commands are to keep a check on other commands and their affect on the database. These commands can annul changes made by other commands by rolling back to original state. It can also make changes permanent.

Command Description
commit to permanently save
rollback to undo change
savepoint to save temporarily

DCL : Data Control Language

Data control language provides command to grant and take back authority.

Command Description
grant grant permission of right
revoke take back permission.

DQL : Data Query Language

Command Description
select retrieve records from one or more table