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.

CommandDescription
createto create new table or database
alterfor alteration
truncatedelete data from table
dropto drop a table
renameto 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.

CommandDescription
insertto insert a new row
updateto update existing row
deleteto delete a row
mergemerging 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.

CommandDescription
committo permanently save
rollbackto undo change
savepointto save temporarily


DCL : Data Control Language

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

CommandDescription
grantgrant permission of right
revoketake back permission.


DQL : Data Query Language

CommandDescription
selectretrieve records from one or more table

Quantitative Aptitude
Reasoning
Programming
Interview