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IS NULL Conditional Expression


The IS NULL conditional expression compares to determine whether the expression specified on the left is NULL, and if it is NULL, returns TRUE and it can be used in the conditional expression. If NOT comes before the NULL keyword, the result of a NOT operation on the result of the IS NULL operation is returned.


expression IS [ NOT ] NULL

  • expression: A single-value column, path expression (ex.: tbl_name.col_name), constant value or arithmetic function that produces a single value can be used. 

SELECT * FROM condition_tbl WHERE salary IS NULL;

           id  name                  dept_name                  salary


            7  'Brown     '          'account'                    NULL


--selecting rows where salary is NOT NULL

SELECT * FROM condition_tbl WHERE salary IS NOT NULL;

           id  name                  dept_name                  salary


            1  'Kim       '          'devel'                   4000000

            2  'Moy       '          'sales'                   3000000

            3  'Jones     '          'sales'                   5400000

            4  'Smith     '          'devel'                   5500000

            5  'Kim       '          'account'                 3800000

            6  'Smith     '          'devel'                   2400000


--simple conparison operation returns NULL when operand is NULL

SELECT * FROM condition_tbl WHERE salary = NULL;

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