Performance of COUNT SQL function

Question

I have two choices when writing an SQL statement with the COUNT function.

1. SELECT COUNT(*) FROM
2. SELE

Answer 1

Performance should not matter because they do 2 different aggregates

• COUNT(*) is all rows, including NULLs
• COUNT(some_column_name), excludes NULL in "some_column_name"

See the "Count(*) vs Count(1)" question for more

Answer 2

No, there is no performance gain in Sql Server.

Answer 3

Option 2 actually counts all the fields where some_column_name is not null. Option 1 counts all the fields where any field is not null. So you might actually get different results out of these two queries. Most of the time you actually want to count all the rows, and then the fastest option, which does not check for any of the fields, is simply SELECT COUNT(1) FROM ...