Data Type: Any
An expression containing string or numeric data.
If the expression passed to IsNull is
True is returned; otherwise,
All variables in
checked for null values. If a null value is found in any one
part of the expression,
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 a
Null value also result in a
Null value. This makes perfect sense.
For instance, if we have an array containing two valid months of
sales data and a
representing the third month’s sales data, the quarter’s sales
data should also be
since accurate data for the quarter is not available.
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 if
varMyVar is null. This occurs because the value of an expression containing ...