SQL Aliases

SQL Aliases

An alias is created with the AS keyword, and is often used to make a column name more readable.

An alias only exists for the duration of that query.

Alias for Columns

The following SQL creates two aliases, one for the CustomerID column and one for the CustomerName column:

Example

SELECT CustomerID AS ID, CustomerName AS Customer

FROM Customers;

Syntax

Alias for column:

<p><code class="sqlHigh">
 SELECT <em>column_name</em> AS <em>alias_name</em><br/>
 FROM <em>table_name;</em></code></p>

Alias for table:

<p><code class="sqlHigh">
 SELECT <em>column_name(s)</em><br/>
 FROM <em>table_name </em>AS <em>alias_name;</em>
</code></p>

Demo Database

Below is a selection from the Customers table used in the examples:

Aliases with Spaces

If you want your alias to contain one or more spaces, like "My Great Products", surround the aliasname with square brackets or double quotes:

Example

SELECT ProductName AS [My Great Products]

FROM Products;

OR:

Example

SELECT ProductName AS "My Great Products"

FROM Products;

Note: Some database systems allows both [] and "", and some only allows one of them.

Concatenate Columns

The following SQL creates an alias named "Address" that combine four columns (Address, PostalCode, City and Country):

Example

 SELECT CustomerName, Address + ', ' + PostalCode + ' ' + City + ', ' + Country
 AS Address

FROM Customers;

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

MySQL Example

SELECT CustomerName, CONCAT(Address,', ',PostalCode,', ',City,', ',Country) AS Address

FROM Customers;

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

Oracle Example

  SELECT CustomerName, (Address || ', ' || PostalCode || ' ' || City || ', ' ||
  Country) AS Address
FROM Customers;

Alias for Tables

The same rules applies when you want to use an alias for a table.

Example

SELECT * FROM Customers AS Persons;

It might seem useless to use aliases on tables, but when you are joining tables, it makes sense.

In the following example, c is the alias for customers and o is for orders, making the query shorter and easier to read:

Example

SELECT c.CustomerName, o.OrderID

FROM customers AS c

JOIN orders AS o ON c.customerID = o.customerID;

You will learn more about SQL Joins in the next chapters.

Aliases are useful when:

• There are more than one table involved in a query
• Functions are used in the query
• Column names are long or not very readable
• Two or more columns are combined together