SQL Alias | AS Keyword

Use Of Sql Alias

Sql Aliases can be very useful for table name when:

• There are more than one table used in a SQL statement.

Sql Aliases can be very useful for column name when:

• Column names are too big or not easy readable.
• SQL Functions are used in the SQL statement with column names like SUM(), COUNT(), or AVG().
• Two or more columns are combined together as a single column in the SQL statement.

Sql Alias | AS Syntax

The below syntax is used to create aliases for column name.

SELECT column_name1 AS column_alias_name1
FROM table_name;

The below syntax is used to create aliases for table name.

SELECT column_name1, column_name2
FROM table_name AS table_alias_name;

Note:

• If the table or column alias_name contains spaces, you must enclose the alias_name with single or double quotes.
• The column alias_name is only valid within the scope of the SQL SELECT statement and It cannot be used in SQL WHERE clause for conditions.

Sample Database Table - Employee

Sample Database Table - Employee_Official

SQL Alias | AS Example for Column Names

The following SQL statement specifies two aliase names, one for the "FName" column and another for the "LName" column, in the "Employee" table.

Tip: It requires single or double quotation marks or square brackets if the alias name contains spaces:

SELECT 
FName As FirstName, 
LName As 'Last Name' 
FROM Employee;

The result of above query is:

In the following SQL statement we combine two columns (FName and LName) and create an alias named "FullName", in the "Employee" table:

SELECT 
FName + " " + LName As FullName 
FROM Employee;

The result of above query is:

Note: To get the SQL statement above to work in MySQL use the following:

SELECT 
CONCAT(FName, " " , LName) As FullName 
FROM Employee;

SQL Alias | AS Example for Table Names

Table alias name mainly used, when selecting columns from multiple tables.

The following SQL statement selects all(ID, FName, LName, Salary) the records from the "Employee" and "Employee_Official" tables.

We use the "Employee" and "Employee_Offical" tables, and give them the table aliases of "e" and "o" respectively:

SELECT 
e.ID, e.FName + " " + e.LName As Name, o.Salary 
FROM Employee As e, Employee_Official o 
WHERE e.ID = o.ID;

The result of above query is:

Note:- There must be a common columns while selecting columns from multiple tables. In the "Employee" and "Employee_Official" both tables contains a common column called "ID".