SQLAliases
SQL Aliases
SQL aliases are used to give a table, or a column in a table, a temporary name.
Aliases are often used to make column names more readable.
An alias only exists for the duration of that query.
An alias is created with theAS keyword.
AS is Optional
Actually, in most database languages, you can skip the AS keyword and get the same result:
Syntax
When alias is used on column:
SELECTcolumn_name ASalias_name
FROMtable_name;
When alias is used on table:
SELECTcolumn_name(s)
FROMtable_nameASalias_name;
Demo Database
Below is a selection from theCustomersandOrders tables used in the examples:
Customers
| CustomerID | CustomerName | ContactName | Address | City | PostalCode | Country |
|---|---|---|---|---|---|---|
| 1 | Alfreds Futterkiste | Maria Anders | Obere Str. 57 | Berlin | 12209 | Germany |
| 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 |
Orders
| OrderID | CustomerID | EmployeeID | OrderDate | ShipperID |
|---|---|---|---|---|
| 10248 | 90 | 5 | 7/4/1996 | 3 |
| 10249 | 81 | 6 | 7/5/1996 | 1 |
| 10250 | 34 | 4 | 7/8/1996 | 2 |
Alias for Columns
The following SQL statement creates two aliases, one for the CustomerID column and one for the CustomerName column:
Using Aliases With a Space Character
If you want your alias to contain one or more spaces, like "My Great Products",surround your alias with square brackets or double quotes.
Example
Using [square brackets] for aliases with space characters:
FROM Products;
Example
Using "double quotes" for aliases with space characters:
FROM Products;
Note: Some database systems allows both [] and "", and some only allows one of them.
Concatenate Columns
The following SQL statement creates an alias named "Address" that combine four columns (Address, PostalCode, City and Country):
Example
FROM Customers;
Note: To get the SQL statement above to work in MySQL use the following:
MySQL Example
FROM Customers;
Note: To get the SQL statement above to work in Oracle use the following:
Oracle Example
FROM Customers;
Alias for Tables
The same rules applies when you want to use an alias for a table.
Example
Refer to the Customers table as Persons instead:
It might seem useless to use aliases on tables, but when you are using more than one table in your queries,it can make the SQL statements shorter.
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 use aliases to make the SQL shorter):
Example
FROM Customers AS c, Orders AS o
WHERE c.CustomerName='Around the Horn' AND c.CustomerID=o.CustomerID;
The following SQL statement is the same as above, but without aliases:
Example
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
