GROUP_ID function in Oracle

by

GROUP_ID is an advanced function that the Oracle database supports. It is used to assign a number to each group resulting from a GROUP BY clause. The GROUP_ID function is supported in the various versions of the Oracle/PLSQL, including, Oracle 12c, Oracle 11g, Oracle 10g and Oracle 9i.

Syntax: 

SELECT column1, column2, ... column_n, GROUP_ID()
FROM tables
WHERE conditions
GROUP BY column1, column2, ... column_n;

Example: 

SELECT SUM(marks), class, extra_marks, GROUP_ID()
FROM students
WHERE extra_marks > 10
GROUP BY class,
ROLLUP (class, extra_marks);

Explanation:
The GROUP_ID function will return 0, for each unique group in the result set. It will return a value greater than 0, if a duplicated group is found.