Code Inspection: Column should be in group by clause

Reports columns that are not in the GROUP BY clause or inside an aggregate function call.

Example (Microsoft SQL Server):

CREATE TABLE t1 (a INT, b INT);
SELECT a, b FROM t1 GROUP BY a;

If you run the SELECT query, you will receive an error because Microsoft SQL Server expects the b column in GROUP BY or used inside an aggregate function. The following two examples will fix the error.

SELECT a, b FROM t1 GROUP BY a, b;
SELECT a, max(b) max_b FROM t1 GROUP BY a;