Is “SELECT COUNT(column)” faster/slower than “SELECT COUNT(*)”? [duplicate]

Answer 1

I tried a few SELECT COUNT(*) FROM MyTable vs. SELECT COUNT(SomeColumn) FROM MyTable with various sizes of tables, and where the SomeColumn once is a clustering key column, once it's in a non-clustered index, and once it's in no index at all.

In all cases, with all sizes of tables (from 300'000 rows to 170 million rows), I never see any difference in terms of either speed nor execution plan - in all cases, the COUNT is handled by doing a clustered index scan --> i.e. scanning the whole table, basically. If there is a non-clustered index involved, then the scan is on that index - even when doing a SELECT COUNT(*)!

There doesn't seem to be any difference in terms of speed or approach how those things are counted - to count them all, SQL Server just needs to scan the whole table - period.

Tests were done on SQL Server 2008 R2 Developer Edition

Answer 2

select count(*) will be slower as it attempts to fetch everything. Specifying a column (PK or any other indexed column) will speed up things as the query engine knows ahead of time what it is looking for. It'll also use an index as opposed to going against the table.