Query sometimes returns incomplete results

[TK]

I have a query that has been working reliably until
recently, but now it frequently loses records from the
resultset. It seems to run properly about half the time,
but sometimes it returns all but 2 or three records that
should be in the results, and it does this without any
indication of an error. The skipped records seem to be
different each time, and I cannot find a pattern to which
records are skipped, but I think the problem went away for
a while when I added several indexes in the underlying
tables.

Any thoughts on what could cause this kind of
inconsistency? It is not very reassuring that the same
query will return different results when run several times
on the exact same data...

 

[TK]

The problem seems to be that the query has not actually
completed even after the record count indicator appears at
the bottom of the result datasheet. If I wait longer, (but
how long is not clear), the query results do actually
complete somewhere in the background, but I need to sort
the resultset to refresh the data, and then the complete
query results are displayed, correct record count and all.
go figure...