Possible to do if .. then atomically without exceptions? (2 replies)

Please see this question on stackoverflow.com:

http://stackoverflow.com/questions/12373009/how-to-avoid-duplicate-keys-with-mysql-and-jpa

To summarize: is it possible to perform the following action atomically without the possibility of deadlock exceptions:

* Query for x (where x has a unique index)
* If x is not found, insert x

If so, how?

Thanks.