How to enforce this constraint in sql server
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Published on 2010-04-21T15:58:41Z
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I have a table called city, and a table called city_city. city_city correlates two city records, so it has a fromcity_id and a tocity_id. I can enforce uniqueness on fromcity_id and and tocity_id through a unique key, but how do I enforce uniqueness so that I cant insert a record if fromcity_id and tocity_id are reversed.
For example, the following records are conceptually the same:
id fromcity_id tocity_id
1 100 200
2 200 100
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