Function IsNull() Foundation
Tests if an expression evaluates to NULL/NIL.
IsNull( <Expression> ) --> lIsNull IsNull( <Expression> , <ReplacementValue> ) --> xValue
If IsNull() is called with a single parameter, IsNull() returns .T. (true) if an expression evaluates to a NULL/NIL value; otherwise, IsNull( ) returns .F. (false).
If the parameter <ReplacementValue> is passed, the function IsNull() returns the value of <ReplacementValue> if <Expression> evaluates to NULL/NIL. Otherwise the value of <Expression> is returned.
The function IsNull() should be used instead of an explicit comparison with NIL wherever <Expression> is related to database operations. Using IsNull() instead of <Expression> != NIL helps to keep businbess logic independent of the underlying database management system due to the fact that all major DBMS vendors support IsNull().
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