SQL - Alias Syntax

You can rename a table or a column temporarily by giving another name known as alias.
The use of table aliases means to rename a table in a particular SQL statement. The renaming is a temporary change and the actual table name does not change in the database.
The column aliases are used to rename a table's columns for the purpose of a particular SQL query.

Syntax:

The basic syntax of table alias is as follows:

SELECT column1, column2.... FROM table_name AS alias_name WHERE [condition];

The basic syntax of column alias is as follows:

SELECT column_name AS alias_name FROM table_name WHERE [condition];

Example:

Consider following two tables, (a) CUSTOMERS table is as follows:

+----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+

(b) Another table is ORDERS as follows:

+-----+---------------------+-------------+--------+ |OID | DATE | CUSTOMER_ID | AMOUNT | +-----+---------------------+-------------+--------+ | 102 | 2009-10-08 00:00:00 | 3 | 3000 | | 100 | 2009-10-08 00:00:00 | 3 | 1500 | | 101 | 2009-11-20 00:00:00 | 2 | 1560 | | 103 | 2008-05-20 00:00:00 | 4 | 2060 | +-----+---------------------+-------------+--------+

Now following is the usage of table alias:

SQL> SELECT C.ID, C.NAME, C.AGE, O.AMOUNT FROM CUSTOMERS AS C, ORDERS AS O WHERE C.ID = O.CUSTOMER_ID;

This would produce following result:

+----+---------+-----+--------+ | ID | NAME | AGE | AMOUNT | +----+---------+-----+--------+ | 3 | kaushik | 23 | 3000 | | 3 | kaushik | 23 | 1500 | | 2 | Ramesh | 25 | 1560 | | 4 | kaushik | 25 | 2060 | +----+---------+-----+--------+

Following is the usage of column alias:

SQL> SELECT ID AS CUSTOMER_ID, NAME AS CUSTOMER_NAME FROM CUSTOMERS WHERE SALARY IS NOT NULL;

This would produce following result:

+-------------+---------------+ | CUSTOMER_ID | CUSTOMER_NAME | +-------------+---------------+ | 1 | Ramesh | | 2 | Ramesh | | 3 | kaushik | | 4 | kaushik | | 5 | Hardik | | 6 | Komal | | 7 | Muffy | +-------------+---------------+