60 SQL - Alias Syntax

You can rename a table or a column in a database temporarily by giving them another pseudo name. This pseudo name is known as Alias. The use of aliases is to address a specific table or a column in an SQL statement without changing their original name in the database. Aliases are created with the AS keyword.

Aliases can be especially useful when working with complex queries involving multiple tables or columns with similar names. By assigning temporary names to these tables or columns, you can make your SQL query more readable and easier to understand.

The SQL Aliasing

Aliases are used to address database tables with a shorter or more meaningful name within an SQL query. The basic syntax of a table alias is as follows.

SELECT column1, column2....
FROM table_name AS alias_name;

Example

Assume we have created a table with name CUSTOMERS in MySQL database using CREATE TABLE statement as shown below −

CREATE TABLE CUSTOMERS (
   ID INT NOT NULL,
   NAME VARCHAR (20) NOT NULL,
   AGE INT NOT NULL,
   ADDRESS CHAR (25),
   SALARY DECIMAL (18, 2),       
   PRIMARY KEY (ID)
);

Following query inserts values into this table using the INSERT statement −

INSERT INTO CUSTOMERS VALUES
(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, 'Hyderabad', 4500.00),
(7, 'Muffy', 24, 'Indore', 10000.00);

The CUSTOMERS table obtained 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	Hyderabad	4500.00
7	Muffy	24	Indore	10000.00

Now, we are creating the second table ORDERS using CREATE TABLE statement as shown below −

CREATE TABLE ORDERS (
   OID INT NOT NULL,
   DATES DATETIME NOT NULL,
   CUSTOMER_ID INT NOT NULL,
   AMOUNT INT NOT NULL,      
   PRIMARY KEY (OID)
);

Following query inserts values into this table using the INSERT statement −

INSERT INTO ORDERS VALUES
(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);

The ORDERS table obtained is as shown below −

OID	DATE	CUSTOMER_ID	AMOUNT
102	2009-10-08 00:00:00	3	3000.00
100	2009-10-08 00:00:00	3	1500.00
101	2009-11-20 00:00:00	2	1560.00
103	2008-05-20 00:00:00	4	2060.00

Now, the following query shows the usage of a table alias. The CUSTOMERS table is aliased as 'C' and the ORDERS table is aliased as 'O' −

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

Output

This would produce the following result −

ID	NAME	AGE	AMOUNT
3	Kaushik	23	3000.00
3	Kaushik	23	1500.00
2	Khilan	25	1560.00
4	Chaitali	25	2060.00

Aliasing Column Names

We can also use an alias for a column name in SQL to give it a different name in the result set of a query. The basic syntax of a column alias is as follows −

SELECT column_name AS alias_name
FROM table_name;

Example

Following is the usage of a column alias. Here, the NAME column is aliased as 'CUSTOMER_NAME' −

SELECT ID AS CUSTOMER_ID, NAME AS CUSTOMER_NAME
FROM CUSTOMERS;

Output

This would produce the following result −

CUSTOMER_ID	CUSTOMER_NAME
1	Ramesh
2	Khilan
3	Kaushik
4	Chaitali
5	Hardik
6	Komal
7	Muffy

Aliasing with Self Join

The SQL Self Join is used to join a table to itself as if the table were two tables. During this process, we need to use alias for one of the tables with a temporary name to avoid misunderstandings. This renaming is done using aliases.

Syntax

Following is the syntax for performing a self-join with aliases −

SELECT column_name(s)
FROM my_table a, my_table b
ON a.join_column = b.join_column;

Example

Now, let us join the CUSTOMERS table to itself using the following Self Join query. Our aim is to establish a relationship among customers on the basis of their earnings. In here, we are using aliases with column names as well as with the table names −

SELECT 
   a.ID, b.NAME as EARNS_HIGHER, 
   a.NAME as EARNS_LESS, 
   a.SALARY as LOWER_SALARY
FROM CUSTOMERS a, CUSTOMERS b
WHERE a.SALARY < b.SALARY;

Output

Output of the above query is as follows −

ID	EARNS_HIGHER	EARNS_LESS	LOWER_SALARY
2	Ramesh	Khilan	1500.00
2	Kaushik	Khilan	1500.00
6	Chaitali	Komal	4500.00
3	Chaitali	Kaushik	2000.00
2	Chaitali	Khilan	1500.00
1	Chaitali	Ramesh	2000.00
6	Hardik	Komal	4500.00
4	Hardik	Chaitali	6500.00
3	Hardik	Kaushik	2000.00
2	Hardik	Khilan	1500.00
1	Hardik	Ramesh	2000.00
3	Komal	Kaushik	2000.00
2	Komal	Khilan	1500.00
1	Komal	Ramesh	2000.00
6	Muffy	Komal	4500.00
5	Muffy	Hardik	8500.00
4	Muffy	Chaitali	6500.00
3	Muffy	Kaushik	2000.00
2	Muffy	Khilan	1500.00
1	Muffy	Ramesh	2000.00