PRB: Using "!=" in a Join Statement Does Not Return Records

• Microsoft Visual FoxPro for Windows, versions 5.0, 5.0a

SYMPTOMS

When you specify a JOIN condition in a SQL Select statement using the ON clause, and you use the not equal sign (!=) with one empty table, the statement does not return any records.

STATUS

This behavior is by design.

MORE INFORMATION

ON Clause with !=

The following syntax does not return all the records from one table that do not have a matching record in the other table:

   SELECT * FROM tbl1 INNER JOIN tbl2 ON tbl1.fld1 != tbl2.fld1

Where Clause with !=

To create a result set that includes all records from one table that do not exist in a second table, use the following syntax:

   SELECT * FROM tbl1 WHERE tbl1.fld1 != tbl2.fld1

   SELECT * FROM tbl1 inner join tbl2 on tbl1.fld1 != tbl2.fld1

   SELECT * FROM tbl1 WHERE tbl1.fld1 != tbl2.fld1

Steps to Reproduce Behavior

Place the following code in a program file and run the code. Note that there are no records returned in the cursor.

   CREATE DATABASE MyTest
   CREATE TABLE tbl1 (fld1 c(10),fld2 c(20))
   CREATE TABLE tbl2 (fld1 c(10), fld2 c(20))
   INSERT INTO tbl1 VALUES('1','Rec1')
   INSERT INTO tbl1 VALUES ('2','Rec2')
   SELECT * INTO CURSOR MyCurse FROM tbl1 inner JOIN tbl2 ON ;
   tbl1.fld1 != tbl2.fld1

   INSERT INTO tbl2 VALUES ('1','tbl2Rec1')
   INSERT INTO tbl2 VALUES ('2','tbl2Rec2')
   SELECT * INTO CURSOR MyCurse FROM tbl1 inner JOIN tbl2 ON ;
   tbl1.fld1 != tbl2.fld1

REFERENCES

For additional information, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q124589
   TITLE     : How to Create a Left-Right Outer Join in FoxPro for Windows