 Boolean ֵָʽǷ񲻰κЧ (Null)

IsNull(expression)
expression ʽ

˵
 expression Ϊ Null IsNull  TrueʽЧݣ IsNull  False expression ɶɣʽκɱе Null ʹʽ True

Null ֵָЧݡNull  Empty ָͬδʼNull 㳤ַ ("") Ҳͬ㳤ַָǿմ

   ʹ IsNull жϱʽǷ Null ֵĳЩʹʽȡֵΪ True IfVar=Null  IfVar<>NullͨΪ FalseΪκΰ Null ıʽΪ NullԱʽĽΪ False
ʾ IsNull Ƿ Null 

Dim MyVar, MyCheck
MyCheck = IsNull(MyVar)   '  False
MyVar = Null   ' Ϊ Null
MyCheck = IsNull(MyVar)   '  True
MyVar = Empty   ' Ϊ Empty
MyCheck = IsNull(MyVar)   '  False
Ҫ
汾 1
