Msg 157, Level 15, State 1, Line 2
An aggregate may not appear in the set list of an UPDATE statement.
This error message appears when you try to use an aggregate function in the SET list of an UPDATE statement.
The T-SQL statement can be parsed, but causes the error at runtime.
Error of the Severity level 15 are generated by the user and can be fixed by the SQL Server user. Since you cannot use an aggregate function in the SET list, you might need to break the single UPDATE statement into multiple smaller ones.
All versions of SQL Server.
IF OBJECT_ID(‘tempdb..#t’) > 0
DROP TABLE #t
CREATE TABLE #t
INSERT INTO #t SELECT 1;
UPDATE #t SET c1 = SUM(c1);
In the above example we try to use the SUM() aggregate function in the SET list of an UPDATE statement. This raises the error.