Re: MERGE Specification

On Fri, 2010-08-06 at 10:28 +0300, Heikki Linnakangas wrote:
> On 06/08/10 10:12, Simon Riggs wrote:
> > So DO NOTHING is the default and implies silently ignoring rows. RAISE
> > ERROR is the opposite.
> >
> > Coding for those seems very easy, its just a question of "should we do
> > it?". DB2 has it; SQL:2008 does not. But then SQL:2008 followed the DB2
> > introduction of AND clauses, and SQL:2011 has so far followed the DB2
> > introduction of DELETE action also.
>
> I see neither DO NOTHING or RAISE ERROR in the documentation of DB2,
> Oracle, or MSSQL server.

Agreed, Oracle and MSSQL server does not have these.

However, DB2 very clearly does have these features

* SIGNAL which raises an error and can be used in place of any action,
at any point in sequence of WHEN clauses. DB2 already supports SIGNAL as
part of SQL/PSM, which we do not, so RAISE ERROR was the nearest
equivalent command for PostgreSQL.

* ELSE IGNORE which does same thing as DO NOTHING, except it must always
be last statement in a sequence of WHEN clauses. DO NOTHING is already a
phrase with exactly this meaning in PostgreSQL, so I suggest that.

--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Training and Services