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.