Name
IsNull Function
Syntax
IsNull(expression
)
expression
Use: Required
Data Type: Any
An expression containing string or numeric data.
Return Value
Boolean (True
or False
).
Description
Determines whether expression
contains is Null
.
Rules at a Glance
If the expression passed to IsNull is
Null
,True
is returned; otherwise, IsNull returnsFalse
.All variables in
expression
are checked for null values. If a null value is found in any one part of the expression,True
is returned for the entire expression.In VBScript, Null is a separate data type that can take on a single value,
Null
. It is used to indicate that data is missing. Because it represents missing data, all expressions that include aNull
value also result in aNull
value. This makes perfect sense. For instance, if we have an array containing two valid months of sales data and aNull
representing the third month’s sales data, the quarter’s sales data should also beNull
, since accurate data for the quarter is not available.
Programming Tips and Gotchas
IsNull is useful when returning data from a database. You should check field values in columns that allow Nulls against IsNull before assigning the value to a collection or other variable. This stops the common “Invalid Use of Null” error from occurring.
IsNull is the only way to evaluate an expression containing a null. For example, the seemingly correct statement:
If varMyVar = Null Then
always evaluates to
False
, even ifvarMyVar
is null. This occurs because the value of an expression containing ...
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