Tom Lane <tgl@sss.pgh.pa.us> writes:
> Michael seems to feel that the tuple count should be nonzero if any
> of the replacement operations did anything at all. This does not
> make a lot of sense at the command tag level ("UPDATE 4" might not
> mean that 4 tuples were updated) but if you look at the definition
> of PQcmdTuples ("returns the number of rows affected by the SQL
> command") it's not so unreasonable. And I can see the point of
> wanting to know whether anything happened.
Close.
It's not so much that I want to know exactly what happened, it's that
I want to know that if PostgreSQL says nothing happened, then I can be
sure that nothing happened, rather than being told that nothing
happened when something happened, and vice versa.
In fact, my suggestion---which might suffer from issues that I am not
aware of, perhaps the ones that led to the patch in the first
place---would be that, given ambiguity, have the system return
something that would cause PQcmdTuples to return an empty string (I'm
assuing this would be a result string with no numbers attached at
all).
It is documented, after all, as being the return value when the system
cannot determine an otherwise correct number, and all of the code I
looked at would, I believe, cope gracefully with it, returning what
I'm guessing (except in the Perl case, where I'm sure) is a sentinel
value indicating, "it worked, but I have no idea how many tuples were
involved".
But I'm not wedded to that---I just don't want to get an answer back
that might lead me off into the woods.
As for the issue of whether the tag is the same or not, I am utterly
pragmatic---I don't use it, and don't really have a way to get to it
from the interfaces I use, so I think the best option is probably
something where the rules to describe it are straightforward to
minimize confusion and support issues. And it should be documented
appropriately.
I mean, even when this is resolved, we should probably be putting
something in the documentation that says that PQcmdTuples can really
only really be depended upon as a tri-state value: 0 ("nothing
happened"), >0 ("something happened"), empty string ("heck if I
know").
Mike.
