Francisco Reyes wrote:
Lew writes:
Strange? Why? Did you expect a particular statistical distribution?
Perhaps
The impression was that one query was returning everything.. and the
other only the records that did not exist in the one table.
you were surprised by the extent of the situation, not thinking there
could be 100 records that didn't match?
Surprised that the outer join actually did ONLY display records that did
not exist in the second table, even though I did not have a where clause
to not list the records with a NULL value.
You only looked at some of the records, not all of them, correct?
Ah, yes, you did say,
I checked a number of them.
Your evaluation of a whole data set by manual examination of a small subset of
the returned results cannot be certain.
Did you try SELECT COUNT(*) to check if the queries differed in the size of
their returned result sets?
That is what I expected, BUT it only returned records that did NOT exist in the
second table. It did not, as far as I could check, return all records.
You mean "as far as you did check". You still do not know the truth of your
assertion that the outer join returned only a subset of the records.
SELECT COUNT( DISTINCT export_messages.export_id )
FROM export_messages
LEFT OUTER JOIN exports ON (export_messages.export_id = exports.export_id);
vs.
SELECT COUNT( DISTINCT export_messages.export_id )
FROM export_messages;
will reveal.
--
Lew
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