FIX: SELECT-SQL with Subselects in WHERE Clause Stops VFP

ID: Q190540

The information in this article applies to:

Microsoft Visual FoxPro for Windows, versions 5.0, 5.0a

SYMPTOMS

When you execute a SELECT-SQL statement, which uses a subquery, when the SELECT executes, Visual FoxPro exits with an Access Violation (under Windows NT) or an Invalid Page Fault (Windows 95).

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

This bug was corrected in Visual FoxPro 6.0.

MORE INFORMATION

Steps to Reproduce Behavior

NOTE: The following causes Visual FoxPro to exit, and you could lose unsaved data.

Run the following code from a program (.prg) file:


CREATE CURSOR cc (KEYF N(1), inr N(3), DATE d)
INSERT INTO cc VALUES (1, 234, DATE())
INSERT INTO cc VALUES (1, 252, DATE()+1)
INSERT INTO cc VALUES (1, 45, DATE()+2)
INSERT INTO cc VALUES (1, 40, DATE() - 2)
INSERT INTO cc VALUES (1, 50, DATE() - 2)
SELECT MAX(inr) AS mx, MIN(inr) AS mn FROM cc INTO CURSOR q1
SELECT v1.DATE, v1.inr, ;

v2.DATE, v2.inr, ;
v1.DATE - v2.DATE AS days, ;
v1.inr - v2.inr AS net ;
FROM cc v1, cc v2 ;
WHERE v1.inr = (SELECT mx FROM q1);
AND v2.inr = (SELECT mn FROM q1)

Under Windows NT 4.0, Visual FoxPro terminates on the SELECT statement with an error like the following:

vfp.exe
Exception: access violation (0xc0000005), Address 0x0044817c

Under Windows 95, Visual FoxPro terminates on the SELECT statement with an error like the following:

VFP caused an invalid page fault in module VFP.EXE at 0137:00440940.

The address (either the 0x0044817c or 0137:00440940 in the preceding example) will vary with the specific Visual FoxPro 5.0x build number.

The error does not occur in Visual FoxPro 3.0x and one record is returned.

Workaround

Adding the IN clause prevents the error from occurring. Here is a possible work around for this problem:


CREATE CURSOR cc (KEYF N(1), inr N(3), DATE d)
INSERT INTO cc VALUES (1, 234, DATE())
INSERT INTO cc VALUES (1, 252, DATE()+1)
INSERT INTO cc VALUES (1, 45, DATE()+2)
INSERT INTO cc VALUES (1, 40, DATE() - 2)
INSERT INTO cc VALUES (1, 50, DATE() - 2)
SELECT MAX(inr) AS mx, MIN(inr) AS mn FROM cc INTO CURSOR q1
SELECT v1.DATE, v1.inr, ;

  v2.DATE, v2.inr, ;
  v1.DATE - v2.DATE AS days, ;
  v1.inr - v2.inr AS net ;
  FROM cc v1, cc v2 ;
  WHERE v1.inr IN (SELECT mx FROM q1);
  AND v2.inr IN (SELECT mn FROM q1)

Additional query words: kbvfp500bug kbVFp500abug kbSQL kbvfp600fix kbdse kbcode

Keywords : kberrmsg
Version : WINDOWS:5.0,5.0a
Platform : WINDOWS
Issue type : kbbug