I have a table with the following columns:

lid      subject id
period   period for sample i.e. day 1, day 30
labdt    date
sample   sample type

there also others, but they are not relevant

For each combination of these fields, there should be 20 rows similiar
to the following; there are 20 different samples:

lid    period   labdt       sample
0001   day 1    01/01/2001  glucose
0001   day 1    01/01/2001  sodium

i need a query that will show me any combination of the above that
does not have exactly 20 rows, ie the combination of lid, period and
labdt is >20 or <20