Order By and Null values in Oracle Database

It has been a long time since I wrote my last post, so I wanted to start again with very basics yet important topic. With this post, I am trying to cover Behavior of NULL values with Order By clause in Oracle database.

By default when we perform "Order by" in ascending order, NULL values are displayed at last.

ngarg@xe> select * from emp order by comm asc, ename asc;

     EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM     DEPTNO
---------- ---------- --------- ---------- --------- ---------- ---------- ----------
      7844 TURNER     SALESMAN        7698 08-SEP-81       1500          0         30
      7499 ALLEN      SALESMAN        7698 20-FEB-81       1600        300         30
      7521 WARD       SALESMAN        7698 22-FEB-81       1250        500         30
      7654 MARTIN     SALESMAN        7698 28-SEP-81       1250       1400         30
      7876 ADAMS      CLERK           7788 23-MAY-87       1100                    20
      7698 BLAKE      MANAGER         7839 01-MAY-81       2850                    30
      7782 CLARK      MANAGER         7839 09-JUN-81       2450                    10
      7902 FORD       ANALYST         7566 03-DEC-81       3000                    20
      7900 JAMES      CLERK           7698 03-DEC-81        950                    30
      7566 JONES      MANAGER         7839 02-APR-81       2975                    20
      7839 KING       PRESIDENT            17-NOV-81       5000                    10
      7934 MILLER     CLERK           7782 23-JAN-82       1300                    10
      7788 SCOTT      ANALYST         7566 19-APR-87       3000                    20
      7369 SMITH      CLERK           7902 17-DEC-80        800                    20

and when we perform "Order by" in descending order, NULL values are displayed at first.

ngarg@xe> select * from emp order by comm desc, ename asc;

     EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM     DEPTNO
---------- ---------- --------- ---------- --------- ---------- ---------- ----------
      7876 ADAMS      CLERK           7788 23-MAY-87       1100                    20
      7698 BLAKE      MANAGER         7839 01-MAY-81       2850                    30
      7782 CLARK      MANAGER         7839 09-JUN-81       2450                    10
      7902 FORD       ANALYST         7566 03-DEC-81       3000                    20
      7900 JAMES      CLERK           7698 03-DEC-81        950                    30
      7566 JONES      MANAGER         7839 02-APR-81       2975                    20
      7839 KING       PRESIDENT            17-NOV-81       5000                    10
      7934 MILLER     CLERK           7782 23-JAN-82       1300                    10
      7788 SCOTT      ANALYST         7566 19-APR-87       3000                    20
      7369 SMITH      CLERK           7902 17-DEC-80        800                    20
      7654 MARTIN     SALESMAN        7698 28-SEP-81       1250       1400         30
      7521 WARD       SALESMAN        7698 22-FEB-81       1250        500         30
      7499 ALLEN      SALESMAN        7698 20-FEB-81       1600        300         30
      7844 TURNER     SALESMAN        7698 08-SEP-81       1500          0         30

What if we want to change this default behavior of Nulls with Order by. Oracle Database provides us a very neat way to handle such situations. By using NULLS FIRST or NULLS LAST option in ORDER BY clause, we can override the default behavior of Null with Order by clause.

For example, I want to sort my data by comm desc and ename asc, but wants that the values comes first in COMM column and then NULL values. I can use "order by comm desc nulls last"

ngarg@xe> select * from emp order by comm desc nulls last, ename asc;

     EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM     DEPTNO
---------- ---------- --------- ---------- --------- ---------- ---------- ----------
      7654 MARTIN     SALESMAN        7698 28-SEP-81       1250       1400         30
      7521 WARD       SALESMAN        7698 22-FEB-81       1250        500         30
      7499 ALLEN      SALESMAN        7698 20-FEB-81       1600        300         30
      7844 TURNER     SALESMAN        7698 08-SEP-81       1500          0         30
      7876 ADAMS      CLERK           7788 23-MAY-87       1100                    20
      7698 BLAKE      MANAGER         7839 01-MAY-81       2850                    30
      7782 CLARK      MANAGER         7839 09-JUN-81       2450                    10
      7902 FORD       ANALYST         7566 03-DEC-81       3000                    20
      7900 JAMES      CLERK           7698 03-DEC-81        950                    30
      7566 JONES      MANAGER         7839 02-APR-81       2975                    20
      7839 KING       PRESIDENT            17-NOV-81       5000                    10
      7934 MILLER     CLERK           7782 23-JAN-82       1300                    10
      7788 SCOTT      ANALYST         7566 19-APR-87       3000                    20
      7369 SMITH      CLERK           7902 17-DEC-80        800                    20

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