BUG: Update Using Subquery with Aggregate Functions

• Microsoft SQL Server version 4.2 for OS/2
• Microsoft SQL Server, versions 4.2, 4.21, and 4.21a

       NT:  880 (4.2)

SYMPTOMS

In an update statement, if you use a subquery to set the value of a column and include one or more aggregate functions with arithmetic operations, an error occurs complaining that the subquery returns multiple values, even if it does not.

For example, the following causes error 512:

   Update t1 set c2 =(select sum(c)*1
      from t2
      where t1.c1=t2.c)

   Update t1 set c2 =(select sum(c)
      from t2
      where t1.c1=t2.c)

CAUSE

SQL Server incorrectly handles arithmetic operations in a subquery that returns aggregate results if the subquery updates a table.

WORKAROUND

One workaround is to move the constant inside the parentheses if the query remains semantically correct. For example, you can rewrite sum(c)*2 as sum(c*2). Otherwise you can break up the query and use intermediate tables to do the updates.

STATUS

Microsoft has confirmed this to be a problem in SQL Server 4.2 for OS/2 and Microsoft SQL Server versions 4.20, 4.21, and 4.21a. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.