SQL aliases are used to temporarily rename a table or a column heading.
SQL Aliases
SQL aliases are used to give a database table, or a column in a table, a temporary name.
Basically aliases are created to make column names more readable.
SQL Alias Syntax for Columns
SELECT column_name AS alias_name
FROM table_name;
SQL Alias Syntax for Tables
SELECT column_name(s)
FROM table_name AS alias_name;
Demo Database
In this tutorial we will use the well-known Northwind sample database.
Below is a selection from the "Customers" table:
| CustomerID | CustomerName | ContactName | Address | City | PostalCode | Country |
|---|---|---|---|---|---|---|
| 2 | Ana Trujillo Emparedados y helados | Ana Trujillo | Avda. de la Constitución 2222 | México D.F. | 05021 | Mexico |
| 3 | Antonio Moreno Taquería | Antonio Moreno | Mataderos 2312 | México D.F. | 05023 | Mexico |
| 4 | Around the Horn | Thomas Hardy | 120 Hanover Sq. | London | WA1 1DP | UK |
And a selection from the "Orders" table:
| OrderID | CustomerID | EmployeeID | OrderDate | ShipperID |
|---|---|---|---|---|
| 10354 | 58 | 8 | 1996-11-14 | 3 |
| 10355 | 4 | 6 | 1996-11-15 | 1 |
| 10356 | 86 | 6 | 1996-11-18 | 2 |
Alias Example for Table Columns
The following SQL statement specifies two aliases, one for the CustomerName column and one for the ContactName column. Tip: It requires double quotation marks or square brackets if the column name contains spaces:
Example
SELECT CustomerName AS Customer, ContactName AS [Contact Person]
FROM Customers;
In the following SQL statement we combine four columns (Address, City, PostalCode, and Country) and create an alias named "Address":
Example
SELECT CustomerName, Address+', '+City+', '+PostalCode+', '+Country AS Address
FROM Customers;
Note: To get the SQL statement above to work in MySQL use the following:
SELECT CustomerName, CONCAT(Address,', ',City,', ',PostalCode,', ',Country) AS Address
FROM Customers;
Alias Example for Tables
The following SQL statement selects all the orders from the customer with CustomerID=4 (Around the Horn). We use the "Customers" and "Orders" tables, and give them the table aliases of "c" and "o" respectively (Here we have used aliases to make the SQL shorter):
Example
SELECT o.OrderID, o.OrderDate, c.CustomerName
FROM Customers AS c, Orders AS o
WHERE c.CustomerName="Around the Horn" AND c.CustomerID=o.CustomerID;
The same SQL statement without aliases:
Example
SELECT Orders.OrderID, Orders.OrderDate, Customers.CustomerName
FROM Customers, Orders
WHERE Customers.CustomerName="Around the Horn" AND Customers.CustomerID=Orders.CustomerID;
Aliases can be useful when:
- There are more than one table involved in a query
- Functions are used in the query
- Column names are big or not very readable
- Two or more columns are combined together
