On 2022-Aug-01, Álvaro Herrera wrote: > > > If <command>MERGE</command> attempts an <command>INSERT</command> > > > and a unique index is present and a duplicate row is concurrently > > > + inserted, then a uniqueness violation error is raised; > > > + <command>MERGE</command> does not attempt to avoid such > > > + errors by evaluating <literal>MATCHED</literal> conditions. > > > > This was a portion of a chang that was committed as ffffeebf2. > > > > But I don't understand why this changed from "does not attempt to avoid the > > error by executing an <command>UPDATE</command>." to "...by evaluating > > <literal>MATCHED</literal> conditions." > > > > Maybe it means to say "..by re-starting evaluation of match conditions". > > Yeah, my thought there is that it may also be possible that the action > that would run if the conditions are re-run is a DELETE or a WHEN > MATCHED THEN DO NOTHING; so saying "by executing an UPDATE" it leaves > out those possibilities. IOW if we're evaluating NOT MATCHED INSERT and > we find a duplicate, we do not go back to MATCHED.
So I propose to leave it as If <command>MERGE</command> attempts an <command>INSERT</command> and a unique index is present and a duplicate row is concurrently inserted, then a uniqueness violation error is raised; <command>MERGE</command> does not attempt to avoid such errors by restarting evaluation of <literal>MATCHED</literal> conditions. (Is "re-starting" better than "restarting"?) -- Álvaro Herrera Breisgau, Deutschland — https://www.EnterpriseDB.com/ Voy a acabar con todos los humanos / con los humanos yo acabaré voy a acabar con todos (bis) / con todos los humanos acabaré ¡acabaré! (Bender)