On 2014-09-29 15:08:36 -0700, Kevin Grittner wrote:
> Andres Freund <andres@2ndquadrant.com> wrote:
> > On 2014-09-29 14:57:45 -0700, Kevin Grittner wrote:
>
> >> The initial implementation could restrict to these exact clauses
> >> and require that the boolean-expression used equality-quals on all
> >> columns of a unique index on only NOT NULL columns.
> >
> > That'll make it really hard to actually implement real MERGE.
> >
> > Because suddenly there's no way for the user to know whether he's
> > written a ON condition that can implement UPSERT like properties
> > (i.e. the *precise* column list of an index) or not.
>
> Well, unless we abandon transactional semantics for other MERGE
> statements, we should have a way that UPSERT logic continues to
> work if you don't match a suitable index; it will just be slower --
> potentially a lot slower, but that's what indexes are for. I don't
> think we need a separate statement type for the one we "do well",
> because I don't think we should do the other one without proper
> transactional semantics.
Wrong. You can't realistically implement the guarantees of UPSERT
without a corresponding UNIQUE index.
Greetings,
Andres Freund
-- Andres Freund http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services