Function NullIf() Foundation

Returns a NIL/NULL value if the two specified expression values are equivalent

NullIf( <Expression> , <Expression> ) --> lEqual
Specifies the expression to be evaluated.

NullIf() returns the first <Expression> if two expressions are not equivalent. If the expressions are equivalent, NullIf() returns a NULL/NIL value.


The function NullIf() can be used to perform the inverse operation of the Coalesce() function. The following pseudo code illustrates a typical scenario for the usage of the function NullIf().

In the sample code below, the function Coalesce() is used to transform data for input/output handling. Lateron the function NullIf() is used to write back changed data to the database field. If data has not been changed, the database field retains its NULL/NIL value.

// display description if given, otherwise display 
// an informational message 
cOutput := Coalesce(FIELD->DESCRIPTION , "(no description available)") 

// - display the value of cOutput 

// - now the user can change the data 

// assign new value or NIL if no data was entered. 
FIELD->DESCRIPTION := NullIf(cOutput,"(no description available)") 


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