SQL query help

hello

i have 2 tables

1 obj :with 2 fields :code and category
2 evt :with 4 fields :seq_number,mp,object,status

how to find all objects (obj_code) that have no expected maintenance (no seq_number with status = A)
for a given maintenance plan (evt_mp)
while the other objects of the same category have one for this mp.

evt_object and obj_code can be join Received on Wed Jun 09 2004 - 07:31:12 CDT