Define Is Null operator

Define Is Null operator.

- To test for nulls, use only the comparison conditions IS NULL and IS NOT NULL.
- If you use any other condition with nulls and the result depends on the value of the null, then the result is UNKNOWN.
- As a null represents a lack of data, a null cannot be equal or unequal to any value or to another null.
- However, Oracle considers two nulls to be equal when evaluating a DECODE function.
- Oracle also considers two nulls to be equal if they appear in compound keys.
- That is, Oracle considers identical two compound keys containing nulls if all the non-null components of the keys are equal.

select * from student
where student_name IS NOT NULL;
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