cluster table

Hi,

I have to make a dunning form with sapscript but all data are stored in MHND table. Because MHND is a cluster table, I can't use a lots of clauses in SELECT like DISTINCT or ORDER BY, etc

What can I do in this situation? There is no other option which can help me? What is the purpose of table MHNK? It seems that it's identical with MHND.

Thank you.