SQL AS Keyword

The AS keyword in SQL is used to create aliases (alternative names) for columns or tables. Aliases make your queries more readable and easier to understand, especially when dealing with complex queries involving joins or multiple tables.

Using AS: Aliases for Columns

Simple Column Aliases

This example creates aliases for 'CustomerID' and 'CustomerName'.

SELECT CustomerID AS ID, CustomerName AS Customer
FROM Customers;
      

ID | Customer
---------------
(CustomerID values) | (CustomerName values)
      

Aliases with Spaces

To use aliases with spaces, you need to enclose them in square brackets or double quotes.

SELECT CustomerName AS Customer, ContactName AS "Contact Person"
FROM Customers;
      

Customer | Contact Person
------------------------
(CustomerName values) | (ContactName values)
      

Creating an Alias from Multiple Columns

This example combines multiple columns ('Address', 'PostalCode', 'City', 'Country') into a single alias named 'Address'.

SELECT CustomerName, Address + ', ' + PostalCode + ' ' + City + ', ' + Country AS Address
FROM Customers;

--MySQL Equivalent:
SELECT CustomerName, CONCAT(Address,', ',PostalCode,', ',City,', ',Country) AS Address
FROM Customers;
      

CustomerName | Address
----------------------------------------------------
(CustomerName values) | (Concatenated address information)
      

Using AS: Aliases for Tables

Table Aliases in a Join

This shows how to use table aliases ('c' for 'Customers' and 'o' for 'Orders') to shorten a query.

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;
      

OrderID | OrderDate | CustomerName
-------------------------------------
(Order IDs) | (Order Dates) | Around the Horn (repeated for each order)