Maxtrix Report Parent Table Column Total

Hi experts,

I am creating a Purchase register report. with the query to use purchase and purchaseitems tables where purchase table is having 1 to many relationship to purchaseitems table.

In matrix report on vatcode (it is a column name) of purchaseitems I want few of purchase table columns and their grand total at the report end , I am getting the total but it is wrong and it seems that the purchase columns grand total get multiple times of corresponding child table records. how can I supress this behaviour.