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What is the difference between COUNT (), COUNT (*) Functions in SQL?

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What is the difference between COUNT (), COUNT (*) Functions in SQL?
posted Aug 5, 2015 by Archana

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1 Answer

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Best answer

COUNT(*):

Will count all the rows in the specified table

COUNT(Column Name)

Returns the number of rows which have a value (NULL values will not be counted)

--Or--

Some combinations of Count function in SQL Server and their description.

COUNT(*) returns the number of items in a group. This includes NULL values and duplicates.
COUNT(1) returns the number of items in a group. This includes NULL values and duplicates.
COUNT(ALL expression) evaluates expression for each row in a group and returns the number of nonnull values.
COUNT(DISTINCT expression) evaluates expression for each row in a group and returns the number of unique, nonnull values.

For return values greater than 2^31-1, COUNT produces an error. Use COUNT_BIG instead.

This is applicable on below versions of SQL Server

SQL Server 2005
SQL Server 2008 R2
SQL Server 2012
SQL Server 2014

answer Aug 6, 2015 by Manikandan J
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