RubyTalk / gmail.com wrote:
> If you are using Rails and migrations
> 
> add_index(:table, [:column1, :column2], :unique => true)
> 
> if not something like this sql
> 
>  CREATE UNIQUE INDEX index_name ON table(column1,column2);
> 
> Becker

Thanks for your help, but the situation in A=1, B=2 or A=2, B=1 that 
wont be accepted if using unique.

My point is that when record(A=1, B=1) was existed in database, any new 
record(A=1, B=1) can not be valided. They can be (A=1, B=2), (A=1, B=3) 
or (A=5, B=1) etc.
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