SQL Tutorial · Chapter 14 of 32
SQL aliases give a column or a table a temporary name that exists only for the duration of one query. A column alias makes result headings readable and names calculated columns; a table alias shortens long table names so joins are easier to write. Aliases are created with the AS keyword, which is optional in most databases but recommended for clarity.
SQL Alias Syntax
-- column alias
SELECT column_name AS alias_name FROM table_name;
-- table alias
SELECT t.column_name FROM table_name AS t;
-- alias with spaces (quote it)
SELECT Amount AS "Order Amount" FROM Orders;Sample Tables
| CustomerID | Name | City | Country |
|---|---|---|---|
| 1 | Anita Sharma | Mumbai | India |
| 2 | John Smith | London | UK |
| 3 | Maria Garcia | Madrid | Spain |
| 4 | Wei Chen | Singapore | Singapore |
| 5 | Emma Brown | Sydney | Australia |
| OrderID | CustomerID | Product | Amount | OrderDate |
|---|---|---|---|---|
| 101 | 1 | Laptop | 1200 | 2026-01-05 |
| 102 | 2 | Mouse | 25 | 2026-01-07 |
| 103 | 1 | Monitor | 300 | 2026-01-12 |
| 104 | 3 | Keyboard | 45 | 2026-02-02 |
| 105 | 6 | Headset | 80 | 2026-02-15 |
| 106 | 4 | Laptop | 1150 | 2026-03-01 |
Example 1: Rename a Column
SELECT Name AS CustomerName, City AS Location
FROM Customers
WHERE Country = 'UK';| CustomerName | Location |
|---|---|
| John Smith | London |
The table column is still called Name; only the heading in this result changes.
Example 2: Name a Calculated Column
Without an alias a calculated column gets an ugly automatic heading such as Amount * 1.18 or ?column?.
SELECT OrderID, Amount, ROUND(Amount * 1.18, 2) AS AmountWithTax
FROM Orders
WHERE Amount > 100;| OrderID | Amount | AmountWithTax |
|---|---|---|
| 101 | 1200 | 1416.00 |
| 103 | 300 | 354.00 |
| 106 | 1150 | 1357.00 |
Example 3: Table Aliases in a Join
Table aliases keep join queries short. Once you alias a table you must use the alias, not the original name, everywhere in that query.
SELECT c.Name, o.Product, o.Amount
FROM Customers AS c
INNER JOIN Orders AS o ON o.CustomerID = c.CustomerID
WHERE o.Amount > 1000;| Name | Product | Amount |
|---|---|---|
| Anita Sharma | Laptop | 1200 |
| Wei Chen | Laptop | 1150 |
Example 4: Alias with Spaces
SELECT Product AS "Product Name", Amount AS "Order Amount"
FROM Orders
WHERE OrderID = 101;| Product Name | Order Amount |
|---|---|
| Laptop | 1200 |
Double quotes are the standard delimiter. MySQL also accepts backticks and SQL Server accepts square brackets.
Example 5: Using an Alias in ORDER BY
SELECT Product, Amount * 1.18 AS WithTax
FROM Orders
ORDER BY WithTax DESC
LIMIT 2;| Product | WithTax |
|---|---|
| Laptop | 1416.00 |
| Laptop | 1357.00 |
Where Can an Alias Be Used?
| Clause | Column alias allowed? | Why |
|---|---|---|
| ORDER BY | Yes | Runs after SELECT |
| WHERE | No (standard) | Runs before SELECT |
| GROUP BY / HAVING | MySQL, PostgreSQL, SQLite: yes; SQL Server: no | Vendor extension |
Works in MySQL, SQL Server, PostgreSQL, SQLite
- AS is optional for column and table aliases in all four; Oracle forbids AS for table aliases, so omitting it there is a portability habit.
- SQL Server also supports
SELECT alias = expression, a non-standard form. - Column aliases cannot be referenced in WHERE in any of the four; repeat the expression or use a subquery.
Alias Naming Conventions
Good aliases read like column headings: TotalRevenue, OrderCount, AvgAmount. Avoid spaces and punctuation so you never need quotes, and avoid reusing a real column name for a different expression, which confuses both readers and the optimizer. For table aliases, the convention is the table’s initial or a short abbreviation (c for Customers, o for Orders), used consistently across a project so any query is instantly readable.
Common Mistakes
- Using an alias in WHERE:
WHERE WithTax > 1000fails; writeWHERE Amount * 1.18 > 1000. - Referring to the original table name after aliasing it in a join.
- Forgetting the comma between two columns, which turns the second column name into an alias of the first.
- Choosing aliases that clash with real column names, making the query ambiguous.
Practice Exercise
- Return City renamed to Town and Country renamed to Nation for all customers.
- Using table aliases c and o, list each customer name with their OrderID for orders in 2026-01.
Show answers
-- 1
SELECT City AS Town, Country AS Nation FROM Customers;
-- 2
SELECT c.Name, o.OrderID
FROM Customers c
JOIN Orders o ON o.CustomerID = c.CustomerID
WHERE o.OrderDate BETWEEN '2026-01-01' AND '2026-01-31';
-- Anita Sharma 101, John Smith 102, Anita Sharma 103Related Chapters
- SQL SELECT – calculated columns that need names
- SQL Joins Introduction – where table aliases shine
- SQL ORDER BY – sorting by an alias
- SQL from Scratch: full course overview
FAQ
Is the AS keyword required for SQL aliases?
No. SELECT Name CustomerName works in every major database. AS simply makes the alias easier to spot, and it is required nowhere except by some style guides.
Can I use a column alias in the WHERE clause?
Not in standard SQL, because WHERE is evaluated before the SELECT list. Repeat the expression in WHERE or wrap the query in a subquery.
Do aliases change the table permanently?
No. An alias exists only for the query in which it is defined. To rename a column permanently use ALTER TABLE.
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