I have a relatively simple query that periodically fails to find the
data it is looking for.

SELECT QUANTITY, M.COMMENT, P.DESCRIPTION1, M.PROGRESS
FROM MRP M, PARTS P
WHERE P.STOCK_CODE = '123456'
AND M.STOCK_CODE=P.STOCK_CODE
AND ((M.PROGRESS > 0) AND (M.PROGRESS < 5))
ORDER BY MDATE, M.CONTRACT ASCENDING

This will periodically return EOF when a valid record exists - both in
an application and via IBExpert

The problem is with (M.PROGRESS > 0). PROGRESS is an integer field
and there is a single valid record with a value of 1.

Changing the condition to (M.PROGRESS >= 1) correctly returns the
record.

If I backing up the database (Server Version: LI-V2.0.0.12748 Firebird
2.0) and restoring it my desktop (Server Version: WI-V2.0.0.12748
Firebird 2.0) it returns the correct record.

On the Linux server using IBExpert to change the value to 2, and then
changing it back to 1 corrects the problem. Have spotted this on 2
records in the last week.

Same plan for both.