T SQL Aliases

T-SQL supports aliases for both columns in the SELECT statement and tables listed in the FROM statement.

You can use the form < table > < alias >, as in C.Customers C or use < table > AS < alias >, as in C.Customers AS C. The < table > AS < alias > format is much more readable.

The convention for table aliases is to shorten the table name to often one letter names like C for Customers that indicate what table is referenced.

Once you give a table an alias you rename the table for the rest of the query and you can’t reference the table by it's full name anymore.

For example the following SQL statement will fail:

SELECT Customers.FirstName, Customers.LastName
FROM Customers AS C

In order for this statement to work it would need to be written as:

SELECT C.FirstName,C.LastName
FROM Customers AS C

You can also create aliases for columns in the SELECT statement the following ways:

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< expression > AS < alias >

Example: FName AS FirstName (I prefer this method because it’s more readable)

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< expression > < alias >

Example: FName FirstName (With this method it can be difficult to tell the difference between a missing comma in SELECT statement and an alias. )

Example: SELECT firstName lastName (This statement would return the value in the firstName column but the column would be named lastName)

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< alias > = < expression >

Example: FName = FirstName