Lookup for Selection Mutlpile Tables

public void lookup()
{
     SysTableLookup        sysTableLookup;
     Query                 query = new Query();
     QueryBuildDataSource  queryBuildDataSource;
     QueryBuildRange qbr;
     CustomerPreferenceTable custPrefTable;
    ;
    select count(ItemId) from custPrefTable where custPrefTable.AccountNum==SalesLine.CustAccount;

    if(str2int(custPrefTable.ItemId)>0)
    {
        //Box::info("Called1");
        sysTableLookup = SysTableLookup::newParameters(tablenum(CustomerPreferenceTable), this);
        queryBuildDataSource = query.addDataSource(tablenum(CustomerPreferenceTable));
        qbr=queryBuildDataSource.addRange(fieldNum(CustomerPreferenceTable,AccountNum));
        qbr.value(SalesLine.CustAccount);//filters the query based on the selected customer account Number from CustomerPreferenceTable
        super();
        sysTableLookup.addLookupfield(fieldnum(CustomerPreferenceTable, ItemId));
        sysTableLookup.parmQuery(query);

        sysTableLookup.performFormLookup();
    }
    else
    {
         sysTableLookup = SysTableLookup::newParameters(tablenum(InventTable), this);
       // Box::info("Called1");
       // qbr=queryBuildDataSource.addRange(fieldNum(InventTable,ItemId));
        //qbr.value(SalesLine.CustAccount);//filters the query based on the selected customer account Number from CustomerPreferenceTable
        queryBuildDataSource = query.addDataSource(tablenum(InventTable));
        super();
        sysTableLookup.addLookupfield(fieldnum(InventTable, ItemId));
        sysTableLookup.parmQuery(query);

        sysTableLookup.performFormLookup();
    }
}