Re: Query for finding keys (IDs) that only have one of two values associated with it

[Rick James]

Here are two solutions. They may differ, based on information about the dataset that you have not shared.

Those with only one:

SELECT post_id, COUNT(*)
FROM tbl
GROUP BY post_id
HAVING COUNT(*) = 1;

Those with _VenueVenue but not _VenueLat:

SELECT a.post_id
FROM tbl AS a
LEFT JOIN tbl AS b ON a.post_id = b.post_id
WHERE a.meta_key = '_VenueVenue'
AND b.meta_key = '_VenueLat'
AND b.post_id IS NULL

That is, do a "self JOIN", with `a` representing VenueVenue and b representing VenueLat, but not finding a VenueLat (IS NULL).

With the first solution, you get only post_id. If you want more than just post_id, use that as a subquery.