andy <andy@xxxxxxxxxxxxxxx> writes:
> I think your comparing apples and oranges. I'll bet that mysql is
> taking a shortcut and testing the value before updating it.
> The update is probably more close to:
> update test set name = 'kevin' where passion = 'soccer' and name <> 'kevin';
Yeah, that seems to be what they're doing. PG does not bother to make
such a test, on the grounds that it would waste more net cycles than it
would save. Most people are not in the habit of issuing lots of no-op
updates.
Also, if you have a case where you think that is what will happen, you
can add the WHERE-condition for yourself; whereas there is no way in
mysql to get rid of the useless test even if you know it's useless.
regards, tom lane
---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match
