Re: MERGE Specification

On Fri, 2008-04-25 at 11:07 +0200, Petr Jelinek wrote:

> Another thing is, the table on which we do SELECT (the one in USING) can 
> be different from target table and we can use columns from that table in 
> INSERT/UPDATE statement (probably one the reasons why spec says the 
> "SELECT" query has to be executed before any changes). How you want to 
> use the "INSERT first" implementation in this scenario ? IMHO you still 
> need to have both implementations in the end. So we probably need to 
> implement the standard one first and then implement our version and put 
> some restrictions of what can be in USING or INSERT part when using it.

We do this:

1. Run using clause,

then for each row

2. NOT MATCHED rules
3. MATCHED

I'm now happy that we can get a spec-compliant end result by always
forcing NOT MATCHED rules to occur before MATCHED rules, when we have at
least one unique index.

--  Simon Riggs 2ndQuadrant  http://www.2ndQuadrant.com