Count of group by statement AX2012 R3

I want to count group by statement values and write control.

There is a table which have 3 fields; ItemId, TaxGroup and TaxItemGroup. Same itemId must have same taxgroup and taxItemGroup values. If lines which have same ItemId have different tax values, i should throw an exception.

I wrote this code but this return number of all records. How can i write this control?

while select count(RecId) from ActivityLineExtraLcl
        group by Itemid, TaxGroup, TaxItemGroup
            where ActivityLineExtraLcl.Amount != 0
if(ActivityLineExtraLcl.RecId > 1 )
      throw error("Same ItemIds can't have different values!");

The logic you're attempting won't work as written and it doesn't really make sense. You can try something like the below. This identifies the actual items. Your code (if it worked) just looks to see if the entire table ActivityLineExtraLcl has any issues.

ActivityLineExtraLcl        ActivityLineExtraLcl;
ActivityLineExtraLcl        ActivityLineExtraLclExists;

while select ItemId from ActivityLineExtraLcl
    group by ItemId
    where ActivityLineExtraLcl.Amount != 0
exists join ActivityLineExtraLclExists
    where ActivityLineExtraLclExists.ItemId         == ActivityLineExtraLcl.ItemId          &&
          ActivityLineExtraLclExists.Amount         != 0                                    &&
         (ActivityLineExtraLclExists.TaxGroup       != ActivityLineExtraLcl.TaxGroup        ||
          ActivityLineExtraLclExists.TaxItemGroup   != ActivityLineExtraLcl.TaxItemGroup)
          
{
    error(strFmt("Item '%1' has different tax values", ActivityLineExtraLcl.ItemId));
}