Q238518: PRB: SQL Select Statement w/Outer Join Clause Adds NULL Values

Article: Q238518
Product(s): Microsoft FoxPro
Version(s): WINDOWS:5.0,5.0a,6.0
Operating System(s): 
Keyword(s): kbDatabase kbSQL kbvfp500 kbvfp500a kbvfp600 KbDBFDBC kbGrpDSFox kbDSupport kbCodeSnipp
Last Modified: 27-JUL-2001

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, versions 5.0, 5.0a, 6.0 
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SYMPTOMS
========

Executing a SQL Select statement using an OUTER JOIN clause results in null
values being inserted into the fields of the output for which no matching record
is found.

RESOLUTION
==========

If the SQL Select statement is being used to output data to a table, one
workaround is to issue an ALTER TABLE command and set the columns of the table
to NOT NULL. The following code illustrates this workaround:

  SELECT ALIAS()
  FOR i=1 TO FCOUNT(ALIAS())
     ALTER TABLE (ALIAS()) ALTER COLUMN (FIELDS(i)) NOT NULL
  ENDFOR

This workaround is implemented in the code example in the MORE INFORMATION
section following.

MORE INFORMATION
================

Steps to Reproduce Behavior
---------------------------

1. Create a program file called OUTJOIN.PRG using the following code:

  SET SAFETY OFF

  CREATE TABLE test1 (pid c(10), nvar1 N(10,2) NULL, dvar2 d, nvar2 N(10,2) NULL, mvar m)
  INSERT INTO test1 VALUES ('ABCDEFGHIK',3,DATE(),3,REPLICATE('ABCDE ',5))
  INSERT INTO test1 VALUES ('ABCDEFGHIJ',3,DATE(),3,REPLICATE('ABCDE ',5))
  INSERT INTO test1 VALUES ('ABCDEFGHIL',3,DATE(),3,REPLICATE('ABCDE ',5))

  CREATE TABLE test2 (pid c(10), nvar1 T, nvar2 Y, fvar1 F(10,2), fvar2 F(10,2))
  INSERT INTO test2 VALUES ('ABCDEFGHIJ',DATETIME(),45,3,4)
  INSERT INTO test2 VALUES ('ABCDEFGHIL',DATETIME(),45,3,4)
  INSERT INTO test2 VALUES ('ABCDEFGHIZ',DATETIME(),45,3,4)

  SELECT test1.pid, test1.nvar1, test1.dvar2, test1.nvar2, test1.mvar, ;
      test2.pid AS testa, test2.nvar1 AS ntesta, test2.nvar2 AS ntestb, ;
      test2.fvar1 AS ftesta, test2.fvar2 AS ftestb ;
      FROM test1 ;
      LEFT OUTER JOIN test2 ;
      ON test2.pid=test1.pid ;
      INTO TABLE test3

  SELECT test2.pid, test2.nvar1, test2.nvar2, test2.fvar1, test2.fvar2, ;
      test1.pid AS testa, test1.nvar1 AS ntesta, test1.dvar2 AS ntestb, ;
      test1.nvar2 AS ftesta, test1.mvar AS ftestb ;
      FROM test1 ;
      RIGHT OUTER JOIN test2 ;
      ON test1.pid=test2.pid ;
      INTO TABLE test4

  SELECT test3
  BROWSE

  SELECT test4
  FOR i=1 TO FCOUNT(ALIAS())
      ALTER TABLE (ALIAS()) ALTER COLUMN (FIELDS(i)) NOT NULL
  ENDFOR
  BROWSE

2. Execute OUTJOIN.PRG.

Note that when the Test3 Browse window appears, the last five columns of the
first row are set to .NULL.

Note that when the Test4 Browse window appears, the last five columns of the
third row are empty.
(c) Microsoft Corporation 1999, All Rights Reserved. Contributions by John Desch,
Microsoft Corporation.


Additional query words:

======================================================================
Keywords          : kbDatabase kbSQL kbvfp500 kbvfp500a kbvfp600 KbDBFDBC kbGrpDSFox kbDSupport kbCodeSnippet kbSQLProg 
Technology        : kbVFPsearch kbAudDeveloper kbVFP500 kbVFP600 kbVFP500a
Version           : WINDOWS:5.0,5.0a,6.0
Issue type        : kbprb
Solution Type     : kbpending

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