Microsoft KB Archive/124589

= How to Create a Left-Right Outer Join in FoxPro for Windows =

Article ID: 124589

Article Last Modified on 10/15/2003

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APPLIES TO


 * Microsoft Visual FoxPro 3.0 Standard Edition
 * Microsoft FoxPro 2.6a Standard Edition

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This article was previously published under Q124589



SUMMARY
You can use a left outer join to find all occurrences of a key value whether or not a matching record exists in the joined table. However, this article shows by example how to find records from both tables without matching records in the corresponding table. The code in this article illustrates a method to produce a complete (left-right) outer join.



MORE INFORMATION
The following code uses two sample tables to:


 * Determine the number of subscribers who ordered each of several publications per month.
 * Display the number of issues per publication generated each month.

The tables have been simplified in this example to contain only the fields necessary for this demonstration. A zero indicates that either no magazines of a particular type were produced or no subscriptions were placed for a particular magazine during the month.

The first table (SUBSCRIB) contains subscription information consisting of the subscription month, the magazine ID, and the subscription count. The second table (PRODUX) contains the subscription month, magazine ID, and number of magazines produced.

Sample Code
******************************************************
 * LR_JOIN.PRG  Left-Right Outer Join Program
 * table structures:    SUBSCRIB         PRODUX
 * Month    N 3   Month     N 3
 * MagID    C 3   MagID     C 3
 * Sub      N 4   Prod      N 5
 * Eliminate blanks from the SUBSCRIB table
 * Sub      N 4   Prod      N 5
 * Eliminate blanks from the SUBSCRIB table
 * Eliminate blanks from the SUBSCRIB table

SELECT * FROM subscrib ; WHERE !EMPTY(sub) ; INTO CURSOR temp1


 * Eliminate blanks from the PRODUX table

SELECT * FROM produx ; WHERE !EMPTY(prod) ; INTO CURSOR temp2


 * Only records containing data in the count fields for either table
 * are valid. The month and magID fields are assumed to be valid.


 * Create the left outer join

SELECT a.*, b.prod FROM temp1 a, temp2 b ; WHERE ALLTRIM(STR(a.Month)) + a.MagID = ; ALLTRIM(STR(b.Month)) + b.MagID ; UNION ; SELECT *, 00000 FROM temp1 ; WHERE ALLTRIM(STR(Month))+MagID NOT IN ; (SELECT ALLTRIM(STR(Month))+MagID FROM temp2) ; ORDER BY 1, 2 INTO CURSOR left


 * Create the right outer join

SELECT a.*, b.sub FROM temp2 a, temp1 b ; WHERE ALLTRIM(STR(a.Month)) + a.MagID = ; ALLTRIM(STR(b.Month)) + b.MagID ; UNION ; SELECT *, 0000 FROM temp2 ; WHERE ALLTRIM(STR(Month))+MagID NOT IN ; (SELECT ALLTRIM(STR(Month))+MagID FROM temp1) ; ORDER BY 1, 2 INTO CURSOR right


 * Combine both joins into the final result

SELECT Month, MagID, Sub, Prod FROM right ; UNION ; SELECT * FROM left INTO CURSOR result

How the Join Works
As the UNION clause expects the structures to be identical, the first part of the combined joins declares the output field list from the RIGHT cursor (which has the structure of Month, MagID, Prod, Sub) in the same order as found in the LEFT cursor (Month, MagID, Sub, Prod).

Additional query words: kbvfp260a kbvfp300

Keywords: kbprogramming KB124589

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