Oracle – Difference Between SELECT COUNT(*) and SELECT COUNT(column)

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I seem to remember that (on Oracle) there is a difference between uttering select count(*) from any_table and select count(any_non_null_column) from any_table.

What are the differences between these two statements, if any?

Best Answer

  • COUNT(*) will include NULLS
  • COUNT(column_or_expression) won't.

This means COUNT(any_non_null_column) will give the same as COUNT(*) of course because there are no NULL values to cause differences.

Generally, COUNT(*) should be better because any index can be used because COUNT(column_or_expression) may not be indexed or SARGable

From ANSI-92 (look for "Scalar expressions 125")

Case:

a) If COUNT(*) is specified, then the result is the cardinality of T.

b) Otherwise, let TX be the single-column table that is the result of applying the <value expression> to each row of T and eliminating null values. If one or more null values are eliminated, then a completion condition is raised: warning- null value eliminated in set function.

The same rules apply to SQL Server and Sybase too at least

Note: COUNT(1) is the same as COUNT(*) because 1 is a non-nullable expression.

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