How to resolve many-to-many join by 2 one-to-many joins

Hi,
I was asked many times how to resolve many to many relationship between two tables. I read to use 2 one -to- many relationships to resolve this. Can some expalin me when many to many relationship occurs between two tables and how to reslove them with practicle examples. Is there any article on this?
Regards,
Nanda Kishore

Hi,
Please check below link.
http://www.forumtopics.com/busobj/viewtopic.php?p=859029&sid=20d79e3df07b0d8b41aadfbd902bb6b2
http://blog.oaktonsoftware.com/2011/04/bridge-tables-and-many-to-many.html
Thanks,
Amit

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Hi,
This sounds like a Top-N Query , where you pick N items (N=1 in this case) off the top of an orderded list. I think you want a separate ordered list for each assignment; the analytic ROW_NUMBER function does that easily.
Since you didn't post CREATE TABLE and INSERT statements for your sample data, I'll use tables from the scott schema to show how this is done.
Say you have a query like this:
SELECT       d.dname
,       e.empno, e.ename, e.job, e.sal
FROM       scott.dept d
JOIN       scott.emp   e ON   d.deptno = e.deptno
ORDER BY dname
;which produces this output:
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ACCOUNTING           7934 MILLER     CLERK           1300
ACCOUNTING           7839 KING       PRESIDENT       5000
ACCOUNTING           7782 CLARK      MANAGER         2450
RESEARCH             7876 ADAMS      CLERK           1100
RESEARCH             7902 FORD       ANALYST         3000
RESEARCH             7566 JONES      MANAGER         2975
RESEARCH             7369 SMITH      CLERK            800
RESEARCH             7788 SCOTT      ANALYST         3000
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SALES                7844 TURNER     SALESMAN        1500
SALES                7499 ALLEN      SALESMAN        1600
SALES                7900 JAMES      CLERK            950
SALES                7698 BLAKE      MANAGER         2850
SALES                7654 MARTIN     SALESMAN        1250Now say you want to change the query so that it only returns one row per department, like this:
DNAME               EMPNO ENAME      JOB              SAL
ACCOUNTING           7782 CLARK      MANAGER         2450
RESEARCH             7876 ADAMS      CLERK           1100
SALES                7499 ALLEN      SALESMAN        1600where the empno, ename, job and sal columns on each row of output are all taken from the same row of scott.emp, though it doesn't really matter which row that is.
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Here's how to code that:
WITH     got_r_num     AS
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     ,     e.empno, e.ename, e.job, e.sal
     ,     ROW_NUMBER () OVER ( PARTITION BY d.dname
                               ORDER BY         e.ename
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     FROM     scott.dept d
     JOIN     scott.emp   e ON   d.deptno = e.deptno
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,       empno, ename, job, sal
FROM       got_r_num
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Adobe Live Chat: http://www.adobe.com/support/chat/ivrchat.html
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How to resolve many-to-many join by 2 one-to-many joins

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