On 2 November 2017 at 22:59, Nico Williams <n...@cryptonector.com> wrote: > On Thu, Nov 02, 2017 at 03:25:48PM -0700, Peter Geoghegan wrote: >> Nico Williams <n...@cryptonector.com> wrote: >> >A MERGE mapped to a DML like this: >> >> This is a bad idea. An implementation like this is not at all >> maintainable. > > Assuming the DELETE issue can be addressed, why would this not be > maintainable?
It would only take one change to make this approach infeasible and when that happened we would need to revert to the full-executor version. One difference that comes to mind is that MERGE doesn't behave the same way as an UPDATE-join, according to SQL:2011 in that it must throw an error if duplicate changes are requested. That would be hard to emulate using a parser only version. I would call it impressively clever but likely fragile, in this case, though I encourage more ideas like that in the future. -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers