当where子句中存在动态条件时，SQL Server查询性能

Question

Let's say we have query A:

SELECT count(1) FROM MyTable WHERE Date_Created < DATEADD(DD, 3, GETDATE())

AND query B:

SELECT count(1) FROM MyTable WHERE Date_Created < '2013-05-24'

When those queries are run, how does the compiler optimize query A? Does it re-evaluate DATEADD and GETDATE for each row in MyTable ?

The reason I am asking is because I ran several tests to see which queries are faster and the result seems to indicate that there's no huge difference in the performance of the two, which is kinda counter-intuitive. Thanks.

Answer 1

GETDATE is a runtime constant and won't be repeatedly re-evaluated.

Chances are that the whole expression with DATEADD will be only evaluated once.