David Alcock tries an experiment:
The question whether to use COUNT(*) or COUNT(1) has been doing the rounds on the internet again, the question this time is whether or not COUNT(*) forces the optimiser to scan all rows or not.
I’m going to query Sales.Orders table of the WideWorldImporters sample database and use a where clause that should take advantage of a non-clustered index on CustomerID.
David looks at
COUNT(1). The story’s slightly different with
COUNT(ColumnName) when there are NULL values afoot.