GROUP_ID distinguishes duplicate groups resulting from a GROUP BY specification. It is useful in filtering out duplicate groupings from the query result. It returns an Oracle NUMBER to uniquely identify duplicate groups. This function is applicable only in a SELECT statement that contains a GROUP BY clause.

If n duplicates exist for a particular grouping, then GROUP_ID returns numbers in the range 0 to n-1.


The following example assigns the value 1 to the duplicate co.country_region grouping from a query on the sample tables sh.countries and sh.sales:

SELECT co.country_region, co.country_subregion,
       SUM(s.amount_sold) "Revenue", GROUP_ID() g
  FROM sales s, customers c, countries co
  WHERE s.cust_id = c.cust_id
    AND c.country_id = co.country_id
    AND s.time_id = '1-JAN-00'
    AND co.country_region IN ('Americas', 'Europe')
  GROUP BY GROUPING SETS ( (co.country_region, co.country_subregion),
                           (co.country_region, co.country_subregion) )
  ORDER BY co.country_region, co.country_subregion, "Revenue", g;

COUNTRY_REGION       COUNTRY_SUBREGION                 Revenue          G
-------------------- ------------------------------ ---------- ----------
Americas             Northern America                    944.6          0
Americas             Northern America                    944.6          1
Europe               Western Europe                     566.39          0
Europe               Western Europe                     566.39          1

To ensure that only rows with GROUP_ID < 1 are returned, add the following HAVING clause to the end of the statement :