NULL Data Type
The NULL data type represents unknown or unavailable data.
Remarks:
- Input formats often return NULL values for input record fields to indicate that the field data is not available in the current log.
- A value of NULL is different from a zero value. In the Log Parser SQL-Like language,
comparison operators in expressions treat
NULL values as the minimum possible values. In other words, all non-NULL values, even
negative numeric values, are always greater than a NULL value.
On the other hand, the MIN and MAX aggregate functions treat NULL values as respectively the maximum and minimum possible values. In other words, the MIN or MAX value between a non-NULL value and a NULL value is always the non-NULL value. - To test for NULL values in a query use IS NULL or IS NOT NULL in the WHERE or HAVING clauses.
See also:
Constant ValuesExpressions