[Cppcms-users] Bizarre prepared statement problem

[<ele...@ex...>]

I'm truly stumped by this SQL query.

This works as expected:

SELECT * FROM af_scheduled_items i INNER JOIN af_scheduled_items_history
h1 ON h1.root_id=i.id WHERE h1.date_fitted <= '2012-05-17 23:59:59' AND
h1.id IN (SELECT max(h2.id) FROM af_scheduled_items_history h2 WHERE
h2.date_fitted <= '2012-05-17 23:59:59' AND h2.root_id=i.id) AND
h1.aircraft_id = ? ORDER BY i.id ASC

Returns 2 rows which is what's expected.

If I replace the h2.date_fitted with ?

SELECT * FROM af_scheduled_items i INNER JOIN af_scheduled_items_history
h1 ON h1.root_id=i.id WHERE h1.date_fitted <= '2012-05-17 23:59:59' AND
h1.id IN (SELECT max(h2.id) FROM af_scheduled_items_history h2 WHERE
h2.date_fitted <= ? AND h2.root_id=i.id) AND h1.aircraft_id = ? ORDER BY
i.id ASC

This returns 1 row.

And if I replace both date_fitted dates with ?

SELECT * FROM af_scheduled_items i INNER JOIN af_scheduled_items_history
h1 ON h1.root_id=i.id WHERE h1.date_fitted <= ? AND h1.id IN (SELECT
max(h2.id) FROM af_scheduled_items_history h2 WHERE h2.date_fitted <= ?
AND h2.root_id=i.id) AND h1.aircraft_id = ? ORDER BY i.id ASC

This returns sometimes 1 row, sometimes 2 rows.

Can someone with enough wisdom explain this?