When a GROUP BY clause is included in an SQL statement, only those columns with a single value for each group can be included.

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When a GROUP BY clause is included in an SQL statement, the result set is grouped by the specified columns. For each group, only one row is returned, and the values for the other columns are aggregated (e.g., SUM, COUNT, AVG). Therefore, only those columns with a single value for each group can be included in the result set.

When a GROUP BY Clause Is Included in an SQL