BUG: IF Statement with Two EXISTS Separated by OR Clause

• Microsoft SQL Server version 4.2 for OS/2
• Microsoft SQL Server, version 4.2

       NT:  544 (4.2)

SYMPTOMS

If one of the SELECT statements is against an empty tableA query that issues an IF EXISTS statement with an OR clause can process incorrectly. The basic logic looks like:

   If exists (SELECT f1 FROM table1 WHERE f1 = "z") OR
      exists (SELECT f1 FROM table2 WHERE f1 = "a")
         select "TRUE"
   else
         select "FALSE"

CAUSE

SQL Server is not correctly evaluating the IF statement when one or more of the tables has no rows.

WORKAROUND

This problem can be avoided by making sure that both tables contain at least one row. An alternate method is to restructure the IF statement to evaluate one of the EXISTS at a time. In the example given above, it would look like the following:

   If exists (SELECT f1 FROM table1 WHERE f1 = "z")
      select "TRUE"
   else if exists (SELECT f1 FROM table2 WHERE f1 = "a")
      select "TRUE"
   else
      select "FALSE"

STATUS

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