ask for review of MERGE

Dear All,

I have just generate a new patch of MERGE command.

One main change in this edition is the removal of RASIE ERROR action from
MEREG, because its semantics is not well defined yet.

I also rewrote the regress test file merge.sql, to make it consistent with
the examples I used in my wiki page.

Some little (error and warning) bugs are fixed.

In this patch, all the main features of MERGE (sublinks, explain, rule and
trigger, inheritance) are not changed. And so is the DO NOTHING action.

I do wish the MERGE command can be added into psql 9.1. And I wonder what
improvement should be made on current edition.

Could you please have a review on this patch, if you have time and interest?

Your feedback will be highly appreciated.

Thanks

Yours Boxuan