I guess that the timestamps reside in field ts, correct?
Then add a preceding load to your SELECT like this:
CONNECT TO W0Process;
LOAD name, date#(ts, 'DD/MM/YYYY hh:mm:ss.f') as ts, [PRESSURE-AC9];
select name,ts ,VALUE AS "PRESSURE-AC9" WIDTH 10 from history(80) where (period=600) and (name='PRESSURE_AC9')
and (request=2) and ts between '01/04/12 00:00:00.0' and '02/04/12 23:59:00.0';
The QlikView (i.e. non-SQL) function date#() forces interpretation of values as dates according to a format string. Should work.
I have already solved it. The problem can be ascribed to an extra blank string in the timestamp format from the database system:
01/09/12 00:00:00.0 versus
It is in QV hardly visible (you need a to have a very very closely look) and the correct format is
date#(ts, 'DD/MM/YYYY hh:mm:ss.f') should be:
date#(ts, 'DD/MM/YYYY hh:mm:ss.f')
Thank you for you help, it has helped me a lot!