NULLIF( )

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The NULLIF function returns a null value if the arguments are equal, otherwise it returns the value of the first argument.

NULLIF (<expression1>, <expression2>)

Description: The COALESCE and NULLIF expressions are common, shorthand forms of use for the CASE expression involving the NULL state. A COALESCE expression consists of a list of value expressions. It evaluates to the first value expression in the list that evaluates to non-NULL. If none of the value expressions in the list evaluates to non-NULL then the COALESCE expression evaluates to NULL.

The NULLIF expression consists of a list of two value expressions. If the two expressions are unequal then the NULLIF expression evaluates to the first value expression in the list. Otherwise, it evaluates to NULL.

Example: The following example demonstrates the use of CASE using the sample employee.ib database:

select NULLIF(department, head_dept) from department

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