Last not null (nnlast)
- Juan Tomás Alonso Nieto (Deactivated)
- Former user (Deleted)
- Former user (Deleted)
Description
Returns the last non-null value found in a specified column for each grouping occurrence. To determine the last value, Devo uses the eventdate time rather than the log time, that is, the date Devo receives it rather than the date it was generated.
If you want to include null values, you can use the Last (last) operation.
How does it work in the search window?
Before being able to perform this operation, you have to group your data. Be aware that the columns used as arguments for the grouping operation will not be available to select as arguments for the aggregation operation.
After grouping the data, select Aggregation in the search window toolbar, then select the Last not null operation. You need to specify one argument:
Argument | Data type |
|---|---|
Last of mandatory | Any |
The data type of the aggregated values will be the same as the data type of the column used as argument.
You cannot repeat the Last not null operation to apply subsequent aggregations. Use the Maximum (max) operation instead to get the same result. Repeating the Last not null operation returns an error because it requires access to the eventdate field. However, this field isn't available for subsequent aggregations.
Example
In the siem.logtrust.web.activity table, we want to get the last non-null IP address value in each 5-minute period. Before aggregating the data, the table must be grouped in 5-minute intervals. Then we will perform the aggregation using the Last not null operation.
The arguments needed for the Last not null operation are:
Last of → responseTime column
Click Aggregate function and you will see the following result:
How does it work in LINQ?
Group your data using the following structure:
group every server period by column1, column2...every client period
Then, use select... as... to add the new column that will show the aggregated values. This is the syntax for the Last not null operation:
nnlast(column)
See Build a query using LINQ to learn more about grouping and aggregating your data using the LINQ language.
Example
You can copy the following LINQ script and try the example above on the siem.logtrust.web.activity table:
from siem.logtrust.web.activity
group every 5m
every 5m
select nnlast(responseTime) as responsetime