SQL SERVER – SELECT Count(1) vs SELECT Count(*)

SQL SERVER – SELECT Count(1) vs SELECT Count(*)

What is the performance differences in these statements?

Let's analyze it: I have a table Employee with records 34395 which we will use to check the performance.

Set Statistics Time On
Go    
Select Count(*) From Employee
Go    
Set Statistics Time Off
Go

I set statistics time on to check the different time taken by query in message window:

I used Count(*), Count(1) and Count(EmployeeId) to evaluate the time, and here is the result:

Count(*)
SQL Server Execution Times:
   CPU time = 46 ms,  elapsed time = 22 ms.

Count(1)
SQL Server Execution Times:
   CPU time = 47 ms,  elapsed time = 15 ms.

Count(EmployeeId)   -- Table Primary key column
Warning: Null value is eliminated by an aggregate or other SET operation.
SQL Server Execution Times:
   CPU time = 31 ms,  elapsed time = 33 ms.

When I am using EmployeeId I am getting a warning so be careful to use the column name when using count, it depends on your requirements