"Christopher Kings-Lynne" <[EMAIL PROTECTED]> writes:
> INSERT INTO table SELECT 1, 'foo' EXCEPT SELECT 1, 'foo' FROM table WHERE
> pkcol=1;
> See? So now that INSERT statement will insert the row if it doesn't exist,
> or insert zero rows if it does. You are then guaranteed that your
> transaction will not fail and rollback, so you can repeat your update, or do
> the insert first and then the update, etc.
Uh, why exactly do you think this is race-free?
It looks fancy, but AFAICS the SELECT will return info that is correct
as of its starting timestamp; which is not enough to guarantee that the
INSERT won't conflict with another transaction doing the same thing
concurrently.
regards, tom lane
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