How to use Grouping clause to handle NULLS in Oracle?

Problem:

You want to use GROUPING() with ROLLUP, CUBE and SETS functions.

Solution

The GROUPING() function accepts a column and returns 0 or 1. This function returns 1 when the column value is null and returns 0 when the column value is non null. However, GROUPING() is used only in queries that use ROLLUP or CUBE. GROUPING() is very useful when you want to display a value when a null would otherwise be returned.

GROUPING() with a Single Column in a ROLLUP

SQL to pass a column to ROLLUP

The last row in the below example will result total/sum of fees. This total is represented as NULL.

Example

SELECT class_id, SUM(fees)
   FROM students
GROUP BY ROLLUP(class_id)
ORDER BY class_id;

Output

The class_id column for the last row is null. WE can use the GROUPING() function to determine whether this column is null, as shown in the following query.

The GROUPING() returns 0 for the rows that have non null class_id values and returns 1 for the last row that has a null class_id.

Example

SELECT  GROUPING(class_id) As grp, class_id, SUM(fees)
FROM students
GROUP BY ROLLUP(class_id)
ORDER BY class_id;

Output

We will now use the CASE statement to put a meaningful value.

Example

SELECT
   CASE GROUPING(class_id)
      WHEN 1 THEN 'Total fees'
      ELSE class_id
  END AS class_group,
  SUM(fees) AS total
FROM students
GROUP BY ROLLUP(class_id)
ORDER BY class_id;

Output

GROUPING() with CUBE

Example

SELECT
  CASE GROUPING(class_id)
    WHEN 1 THEN 'Total Salaries'
    ELSE class_id
  END AS job_group,
  SUM(fees) AS total_fees
FROM students
GROUP BY CUBE(class_id)
ORDER BY class_id;

Output

The GROUPING SETS clause typically offers better performance than CUBE. Therefore, you should use GROUPING SETS as your first option rather than CUBE wherever possible.

GROUPING SETS Clause

Example

SELECT department_id, class_id, SUM(fees) AS total_fees
FROM students
GROUP BY GROUPING SETS(department_id, class_id)
ORDER BY department_id, class_id;

Output

Data Preparation: Data used for the problem is shown below. The data is completely made up for demonstration purpose.

Example

DROP TABLE students;
COMMIT;

CREATE TABLE students
    ( student_id    NUMBER(6)
    , first_name     VARCHAR2(20)
    , last_name      VARCHAR2(25) CONSTRAINT  stu_last_name_nn  NOT NULL
    , email          VARCHAR2(40) CONSTRAINT  stu_email_nn  NOT NULL
    , phone_number   VARCHAR2(20)
      , join_date      DATE CONSTRAINT           stu_join_date_nn  NOT NULL
    , class_id         VARCHAR2(20) CONSTRAINT stu_job_nn  NOT NULL
    , fees           NUMBER(8,2)
    , professor_id     NUMBER(6)
    , department_id  NUMBER(4)
    , CONSTRAINT     stu_fees_min CHECK (fees > 0)
    , CONSTRAINT     stu_email UNIQUE (email)
    ) ;

Example

CREATE UNIQUE INDEX stu_id_pk ON students (student_id) ;
INSERT INTO students VALUES (100,'SMITH','JAMES','SMITH.JAMES@notreal.com','111.111.1245',TO_DATE('17-06-2003','DD-MM-YYYY'),'INS_CHAIRMAN',24000,NULL,NULL);
INSERT INTO students VALUES (101,'JOHNSON','JOHN','JOHNSON.JOHN@notreal.com','111.111.1246',TO_DATE('21-09-2005','DD-MM-YYYY'),'INS_VP',17000,100,90);
INSERT INTO students VALUES (102,'WILLIAMS','ROBERT','WILLIAMS.ROBERT@notreal.com','111.111.1247',TO_DATE('13-01-2001','DD-MM-YYYY'),'INS_VP',17000,100,90);
INSERT INTO students VALUES (103,'BROWN','MICHAEL','BROWN.MICHAEL@notreal.com','111.111.1248',TO_DATE('03-01-2006','DD-MM-YYYY'),'INS_STAFF',9000,102,60);
INSERT INTO students VALUES (104,'JONES','WILLIAM','JONES.WILLIAM@notreal.com','111.111.1249',TO_DATE('21-05-2007','DD-MM-YYYY'),'INS_STAFF',6000,103,60);
INSERT INTO students VALUES (105,'MILLER','DAVID','MILLER.DAVID@notreal.com','111.111.1250',TO_DATE('25-06-2005','DD-MM-YYYY'),'INS_STAFF',4800,103,60);
INSERT INTO students VALUES (106,'DAVIS','RICHARD','DAVIS.RICHARD@notreal.com','111.111.1251',TO_DATE('05-02-2006','DD-MM-YYYY'),'INS_STAFF',4800,103,60);
INSERT INTO students VALUES (107,'GARCIA','CHARLES','GARCIA.CHARLES@notreal.com','111.111.1252',TO_DATE('07-02-2007','DD-MM-YYYY'),'INS_STAFF',4200,103,60);
INSERT INTO students VALUES (108,'RODRIGUEZ','JOSEPH','RODRIGUEZ.JOSEPH@notreal.com','111.111.1253',TO_DATE('17-08-2002','DD-MM-YYYY'),'CL_PHY',12008,101,100);
INSERT INTO students VALUES (109,'WILSON','THOMAS','WILSON.THOMAS@notreal.com','111.111.1254',TO_DATE('16-08-2002','DD-MM-YYYY'),'CL_MATH',9000,108,100);
INSERT INTO students VALUES (110,'MARTINEZ','CHRISTOPHER','MARTINEZ.CHRISTOPHER@notreal.com','111.111.1255',TO_DATE('28-09-2005','DD-MM-YYYY'),'CL_MATH',8200,108,100);
INSERT INTO students VALUES (111,'ANDERSON','DANIEL','ANDERSON.DANIEL@notreal.com','111.111.1256',TO_DATE('30-09-2005','DD-MM-YYYY'),'CL_MATH',7700,108,100);
INSERT INTO students VALUES (112,'TAYLOR','PAUL','TAYLOR.PAUL@notreal.com','111.111.1257',TO_DATE('07-03-2006','DD-MM-YYYY'),'CL_MATH',7800,108,100);
INSERT INTO students VALUES (113,'THOMAS','MARK','THOMAS.MARK@notreal.com','111.111.1258',TO_DATE('07-12-2007','DD-MM-YYYY'),'CL_MATH',6900,108,100);

COMMIT;

Kiran P

Updated on: 05-Dec-2020

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