Question

I have two varchar columns (ColA, ColB) in a single table (Table1)

Is there a way to craft a constraint that would prevent the same value from appearing in both ColA and ColB?

Example

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Original Table:

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| Col A    |   Col B  |
-----------------------
| Alice    |   Bob    |
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Insert Command that I would like to fail

Insert into Table1 values ('Bob', 'Jill')

Undesired Result

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| ColA     |   ColB   |
-----------------------
| Alice    |   Bob    |   <-- Bob In Col B
-----------------------
| Bob      |   Jill   |   <-- Bob in Col A
-----------------------

Answer 1

You would need to implement this constraint logic as a Trigger.