What will be the output of below query?

Select * from employee_master where employee_code = null;

Answer:

It will NOT return any records.Because Equal(=) sign is a comparison operator used with string/integer/double/decimal or any other data-types BUT not with NULL values.

Because Null means no data or absence of data.
If we want to fetch rows,then we have to modify query as

Select * from employee_master where employee_code Is Null;

Then it will fetch record which have NULL values.