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 |