SQL Null Operations

Null Operations

Null concept in Oracle:-Every null is unique and never equal to another null

Mathematical Concept:-Result will be null on any mathematical operation on null. 
Example:-
null+10=null
null/10=null
null*5=null
null-12=null
That is why every null is unique and never equal to another null

Queries with Null:-
Examples:-
select null+10 from dual;
select null*10 from dual;
select null/5 from dual;
select null-5 from dual;
select null+null from dual;

Result will be null for all above queries.

Oracle Function on null value column:-Every Oracle function treats null values as 0 (by internal nvl function) 
select sum(comm) from emp;

Mathematical Operation without Oracle function:-
Example:-
select sal,comm, sal+comm from emp;

Treating Null value with nvl function:-
Example:-
select sal,comm, sal+nvl(comm,0) from emp;

Data selection from null value column:-

Example:-
select * from emp where comm=null;

Note:-result will be no record this null is never equal to any other null available on column..
Oracle has provided "is" operator for data selection from null values column

Example:-
select * from emp where comm is null;
select * from emp where comm is not null;