Returns true (.T.) if an expression evaluates to a null value; otherwise, ISNULL(В ) returns false (.F.).
ISNULL(eExpression) |
Parameters
- eExpression
- Specifies the expression to evaluate.
Return Value
Logical
Remarks
Use ISNULL(В ) to determine if the contents of a field, memory variable, or array element contains a null value, or if an expression evaluates to a null value.
Example
In the following example, ISNULL(В ) is used to check for a null value.
В | Copy Code |
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STORE .NULL. TO mNullvalue && Store a null value to a memory variable CLEAR ? mNullvalue && Display the value of the memory variable ? ISNULL(mNullvalue) && Returns .T., indicating a null value ? TYPE('mNullvalue') && Returns L, indicating a logical value ? (mNullvalue = .NULL.) && Returns .NULL., bad test for null values |