Does COUNT(*) Always Return a Value, Even with No Matching Records?

Is the

*COUNT() function always guaranteed to return a result? **

Can the COUNT(*) aggregate function return results under any circumstances? Even if the query condition does not match any record in the table?

Answer:

Yes, COUNT() will always return a numeric result, even if the query does not retrieve any matching records. Unlike other aggregate functions like MAX or SUM, in which case the return value is NULL, COUNT() is unique in that it always returns 0.

This is because COUNT(*) operates on the entire table, regardless of the conditions specified. It counts the total number of rows in the table even if no record meets the criteria.

Influence:

1. No validation required: COUNT(*) is guaranteed to return a result without validation since it always provides a numeric value.
2. Impact of grouping: COUNT(*) behaves differently if the query contains a GROUP BY clause. In this case, it counts the number of rows for each grouping and returns no results if no grouping meets the criteria.
3. Standards Conformance: According to the ANSI standard, the behavior of COUNT(*) without a GROUP BY clause applies to all major relational database management systems (RDBMS).

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