mo.notono.us

Monday, May 02, 2005

SQL: The myth of COUNT(FooID)

There is a popular ongoing myth about the performace benefit of specifying an ID when using the COUNT function in SQL. For example, Darrel Norton is normally on the ball about stuff, but here he is just wrong.

SELECT COUNT(FooID) FROM Foo
is not faster than
SELECT COUNT(*) FROM Foo

As the documentation states:

COUNT(*) does not require an expression parameter because, by definition, it does not use information about any particular column. COUNT(*) returns the number of rows in a specified table without eliminating duplicates. It counts each row separately, including rows that contain null values.

Labels:

0 Comments:

Post a Comment

Links to this post:

Create a Link

<< Home