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Avoid referring Column B to Column A and viz versa

Posted on 2007-11-14
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Last Modified: 2011-10-03
I want to avoid corss referring Column B to Column A and viz versa. I have a Column ( B ) refering to Column (A).  The following cases are fine
Col A Col B
1          2
2          3
3

but the following cases are not fine
Col A Col B
1          1
2          3
3          2

Can i do this in by using any database constraint?
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Question by:x1877
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6 Comments
 
LVL 143

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 20279924
what about this:
Col A Col B
1          2
2          3
3          1

(ie the third row closing the "circuit" ?
0
 
LVL 14

Expert Comment

by:twoboats
ID: 20279992
To Angel's point - it's about travesing a network, to decide if it has rows. I did once write code (don't have it) that would deal with any number of levels in 2 passes. Couldn't do it in 1 pass (unless number of levels was known & fixed). Was a chunk of nightmarish code, so haven't kept it. Probably best achieved in a loop.
0
 
LVL 14

Expert Comment

by:twoboats
ID: 20279999
should read

decide if it has loops
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Author Comment

by:x1877
ID: 20280056
angelIII:
Sorry according to busines logic even thats not possible. In that way my example is not perfect.
I am trying to achive the following

Col A Col B
1          2
2          
3          4
4
5           4
Means only 1 parent and 1 child or 1 parent and many children. No grandchild
0
 
LVL 14

Accepted Solution

by:
twoboats earned 2000 total points
ID: 20280140
Don't think you can do it in a constraint, butr should be achievable in a trigger using self joins
0
 

Author Comment

by:x1877
ID: 20358627
trigger not tried...planning to do it using front end code.
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