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I'm running a query like this in MSSQL2008: select count(*) from t1 inner join t2 on t1.id = t2.t1_id inner join t3 on t1.id = t3.t1_id Assume t1.id has a NOT NULL constraint. Since they're inner joins and t1.id can never be null, using count(t1.id) instead of count(*) should produce the exact same end result. My question is: Would the performance be the same? I'm also wondering whether the joins could affect this. I realize that adding or removing a join will affect both performance and the length of the result set. Suppose that without changing the join pattern, you set count to target only one table. Would it make any difference? In other words, is there a difference between these two queries: select count(*) from t1 inner join t2 on t1.id = t2.t1_id select count(t1.*) from t1 inner join t2 on t1.id = t2.t1_id COUNT(id) vs. COUNT(*) in MySQL answers this question for MySQL, but I couldn't find answers for MS-SQL specifically, and I can't find anything at all that takes the join factor into account. NOTE: I tried to find this information on both Google and SO, but it was difficult to figure out how to word my search.

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