Oracle NULL

In Oracle NULL means absence of data. A NULL can be assigned but it cannot be equated with anything. NULL cannot be equated with NULL itself. NULL is one of the confusing feature in Oracle.

Examples :-

Consider below table SALARY with two columns NO and SAL. In 3rd and 4th rows SAL is NULL.

1) List all records with SAL is NULL

select * from salary where sal is null;

NO         SAL
———- ———-
3            NULL
4            NULL

Note :-   In SQL it will represent as is null;

2)  List all records with SAL is not NULL

select * from salary where sal is not null;

NO          SAL
———- ———-
1              2000
2              3000
5              1000

3)  Insert statement with NULL

insert into salary(no,sal) values (6,null);

4) Deleting all records with SAL as NULL

delete from salary where sal is null; 

5) Update statement with NULL

update salary sal = null where no = 5;

6) NULL cannot be equated with NULL itself

select * from salary where null = null;

no rows selected