sql server - Difference between select count(*) from and select count('quoted string') -

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I'm curious about that, some time ago someone had told me that a count ('quoted strin' Code> instead of count (*)

I mean, use the select count ('quoted string') instead of Select the count (*), and the reason for this was that count (*) goes through all the columns and reduces the performance, others have told me that there is a difference Is not ... but if True, does this mean that the count ('cited string') is equal to computation against any of the columns?

Thanks. < / Div>

Count ('any quoted string') or any static expression or literal equivalent. There is no need to even reach the column.

To calculate total rows (cardinality) compared to the count There is better and affect the right for the latter to zero values.

In practice, there is no difference between counting (1) and count (*) (without quotation) because the Optimizer counts on request for the number of rows on any database of salt (* ), And does not reach all columns as one can be expected.

The difference count (1) / count (*) / count ('*') is between the vs count (the colonel), where later, the value for the call will be searched for the empty rows.

This ANSI is specified by the SQL standard.

Personally, I think counting (1) or count (*) are acceptable, but the count ('*') is a bad form, and is probably confused, and / or born of illusion The first place is. I have never really seen the use of it, and if someone thinks that this is a demonstration, then it is generally unaware of the effect of continuous expression.

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