SQL - Alias

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 the 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 the following result:

+----+----------+-----+--------+

| ID | NAME     | AGE | AMOUNT |

+----+----------+-----+--------+

|  3 | kaushik  |  23 |   3000 |

|  3 | kaushik  |  23 |   1500 |

|  2 | Khilan   |  25 |   1560 |

|  4 | Chaitali |  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 the following result:

+-------------+---------------+

| CUSTOMER_ID | CUSTOMER_NAME |

+-------------+---------------+

|           1 | Ramesh        |

|           2 | Khilan        |

|           3 | kaushik       |

|           4 | Chaitali      |

|           5 | Hardik        |

|           6 | Komal         |

|           7 | Muffy         |

+-------------+---------------+