Max over partition by excluding certain values

I have two tables

table1:Messagethread,opendate,closedate,threadsection

table2:Messageid,Messagethread, messagetitle,messagedate,messageparent.

I would like to dispaly the following columns

threadid, threadsection,messagetitle (for all), max message date but (only thoses with messageparent=0), count (messageid but only thoses with messageparent=0), open and close date

 how to select only those records with messageparent=0 for the max and count functions but display the other columns for all records

sz