HAVING in EXISTS-clause ...

Hello PostgreSQL user,

we're haveing some trouble when doing the following commands:

a) This statement works very well ...

SELECT AO,AT,AV FROM P3AT
GROUB BY AO
HAVING COUNT(*)>1


b) This statement works very well ...

SELECT AO,AT,AV FROM P3AT AS OAT 
WHERE EXISTS(  SELECT AO FROM P3AT  WHERE    AO = OAT.AO  GROUB BY AO)

c) This statement does NOT work. It gives an error message:  "rewrite: aggregate column of view must be ar rigth side
inqual"
 

SELECT AO,AT,AV FROM P3AT AS OAT
WHEREEXISTS(  SELECT AO FROM P3AT  WHERE    AO = OAT.AO  GROUP BY AO  HAVING COUNT(*) = 8)

The meaning of the statement is: return the result as triples, but
make sure, that you return only these results, where you have 
eight result rows available for each AO.

Perhaps someone may help me !?

Marten