Is there a performance difference using AS keyword in SQL?

Question

I'm working on a project in which the previous programmer seems to have loved using the AS keyword in the SELECT part of queries. I really don't like how it's written but if there is no performance difference I won't change existing code.

My tests did give a slight advantage to not using the AS keyword but I'm clueless on how to properly test it(I ran the different queries using Navicat)

And maybe there is also a difference between different types of databases and engines. I'm using MySQL InnoDB.

Simplified query:

SELECT DISTINCT
 `sometable`.`id` AS `id`,
 `sometable`.`name` AS `name`,
 `sometable`.`description` AS `description`,
 `sometable`.`price` AS `price`,
 `sometable`.`size` AS `size`,
 `sometable`.`area` AS `area`,
 `sometable`.`center` AS `center`
FROM `sometable`

• HABO: Since you are only changing the metadata, i.e. the name of the returned columns, it doesn't affect each row as it is processed. I'd expect the overhead to be inconsequential.

Answer 1

I wouldn't expect much if any noticeable overhead as all that is doing is aliasing the name of the column in the result set.

The question I would ask however, is why it's being done in the first place? All I can think of is to prevent the code which uses the query breaking if a column is renamed (as long as the alias isn't changed).

• René: I have no idea why it was done, I suppose there is no good reason to it. I wonder, how would it not break this code if a column is renamed? You would still have to rename the key in the query itself so you could add the AS old_key when you do that. And please future programmers, add a comment why you added the alias and or changed the column name.
• Trevor Pilley: Well I suppose that depends on where the query used, I was thinking that if it was in a stored procedure for example, if the column name in the table was changed, as long as the alias remained the same, the results of the stored procedure would remain consistent...
• René: I didn't know/realized a stored procedure would do that. Thanks. Sadly, this is mysql_* in php.