PRB: SQL Select Statement Using an Outer Join Clause Adds NULL Values to the Output

• Microsoft Visual FoxPro for Windows, versions 5.0, 5.0a, 6.0

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 

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.

Additional query words:

Keywords : kbDatabase kbSQL kbVFp500 kbVFp500a kbVFp600 KbDBFDBC kbGrpFox kbDSupport kbCodeSnippet
Version : WINDOWS:5.0,5.0a,6.0
Platform : WINDOWS
Issue type : kbprb