Re: MERGE vs REPLACE

Martijn van Oosterhout wrote:
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> On Wed, Nov 16, 2005 at 11:37:46AM -0500, Bruce Momjian wrote:
> > 
> > Interesting approach.  Actually, we could tell the user they have to use
> > BEGIN;LOCK tab before doing MERGE, and throw an error if we don't
> > already have a table lock.
> 
> The bit I'm still missing is why there needs to be a lock at all. The
> SQL standard doesn't say anywhere that concurrent MERGE operations
> can't conflict. It seems to me that standard visibility rules apply. If
> neither MERGE statement can see the results of the other, then they
> will both INSERT. If you don't have a UNIQUE constraint to prevent this
> then what's the problem?

I assume they want MERGE because they don't want duplicates.  If they
don't care, they would have used INSERT.

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