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7.16.3 NULLIF

NULLIF(value1, value2)

The NULLIF function returns a null value if value1 equals value2; otherwise it returns value1. This can be used to perform the inverse operation of the COALESCE example given above:

SELECT NULLIF(value, '(none)') ...

In this example, if value is (none), null is returned, otherwise the value of value is returned.