code: def aggregate(self, opTable, group_by_cols, meas):
          
          self.sql_text += "DROP TABLE " + opTable + ";\n"
          self.sql_text += "CREATE TABLE " + opTable + " AS (\n"
          self.sql_text += "    SELECT " + group_by_cols + ", " + meas + " AS result \n"
          self.sql_text += "    FROM " + self.fact_table + " GROUP BY " + group_by_cols + "\n"
          self.sql_text += ");\n"
docs: Create an aggregate table grouped by col showing meas
          The meas is something like "sum(in)" or "count(*)"
          RETURNS:
              DROP TABLE C_AGG_PRODUCT;
              CREATE TABLE C_AGG_PRODUCT AS (
                  SELECT PRODUCT, sum(AMOUNT) AS result 
                  FROM C_SALES GROUP BY PRODUCT
              );