SQL Aliases: Rename Columns and Tables With AS

An alias is a temporary name you give to a column or a table inside one query. Aliases make results easier to read and long queries easier to write. They do not change anything in the database.

The example table#

Column aliases#

Put AS and a new name after a column or expression:

SELECT name AS employee_name,
       salary AS monthly_salary
FROM employees
WHERE department = 'Sales';

employee_name | monthly_salary
--------------+---------------
Asha          | 52000
Priya         | 61000

Aliases matter most for calculations. Without one, the database invents a column name such as salary * 12 or ?column?, which is awkward to read and to use from application code.

SELECT name, salary * 0.10 AS bonus
FROM employees
ORDER BY bonus DESC
LIMIT 3;

name  | bonus
------+------
Meera | 8100
Ravi  | 7800
Priya | 6100

Aliases with spaces#

If an alias contains spaces or capital letters you want to keep, wrap it in double quotes:

SELECT name, salary * 12 AS "Yearly Salary"
FROM employees
ORDER BY "Yearly Salary" DESC
LIMIT 2;

name  | Yearly Salary
------+--------------
Meera | 972000
Ravi  | 936000

The AS keyword is optional#

SELECT salary * 12 yearly works the same as SELECT salary * 12 AS yearly. Writing AS is clearer and avoids a classic bug: if you forget a comma between two columns, SELECT name salary silently becomes "the name column, aliased as salary".

Table aliases#

You can also give a table a short name, then use it to prefix columns:

SELECT e.name, e.city
FROM employees AS e
WHERE e.salary > 60000;

name  | city
------+----------
Ravi  | Bengaluru
Meera | Pune
Priya | Delhi

With one table this only saves a little typing. With JOINs, table aliases become essential, because several tables can have columns with the same name:

SELECT c.name, o.amount
FROM customers c
JOIN orders o ON o.customer_id = c.customer_id
ORDER BY o.amount DESC;

name | amount
-----+-------
Ravi | 560
Asha | 250
Asha | 120

Here c and o make it obvious which table each column comes from. Oracle does not allow AS before a table alias, so writing customers c works everywhere.

Where can you use a column alias?#

Aliases are created in the SELECT step. Recall the order SQL processes a query:

FROM → WHERE → GROUP BY → HAVING → SELECT → ORDER BY → LIMIT

So an alias can be used in ORDER BY (which runs after SELECT), but cannot be used in WHERE (which runs before it) in most databases:

-- Error in PostgreSQL, SQL Server and Oracle: column "yearly" does not exist
SELECT name, salary * 12 AS yearly
FROM employees
WHERE yearly > 700000;

Repeat the expression instead:

SELECT name, salary * 12 AS yearly
FROM employees
WHERE salary * 12 > 700000;

name  | yearly
------+-------
Ravi  | 936000
Meera | 972000
Priya | 732000

Common mistakes#

Practice#

SELECT e.name AS employee,
       e.salary * 1.05 AS new_salary
FROM employees e
WHERE e.salary * 1.05 > 60000
ORDER BY new_salary DESC;

employee | new_salary
---------+-----------
Meera    | 85050
Ravi     | 81900
Priya    | 64050

Key takeaway#