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NULL
PQL recognizes IS NULL and IS NOT NULL
in exactly the same way as SQL does.
Examples
- Example #1: Query includes null values
- Example #2: Query excludes null values
- Example #3: Query excludes null systems
Example #1: Query includes null values
Here is a broad query that reports the status of free memory from all devices:
SELECT status/memory_free FROM /network/device
When this query is run against a database that contains devices without all
of the requested information, the result includes several IS NULL
values:
row:
status/memory_free: null
row:
status/memory_free: null
row:
status/memory_free: null
row:
status/memory_free:
memory_free: 355516416
Example #2: Query excludes null values
You can focus the query and avoid cluttering the result with
the IS NULL values by running a query like this:
SELECT status/memory_free FROM /network/device WHERE status/memory_free IS NOT NULL
When this query is run against the same data as above, the result is much more specific:
row:
status/memory_free:
memory_free: 355516416
Example #3: Query excludes null systems
You can focus the query and avoid cluttering the result with
the IS NULL values by running a query like this:
SELECT nvl(
system/name,
system/dns_name
) as "Name",
nvl(
system/model,
system/class,
wmi/win32_computersystem/domainrole
) as "Type",
interface/inet/ip_address as "IP Address",
last_seen
FROM /network/device
WHERE system IS NOT NULL
Depending on your database, this query finds something like the following. Note that although there are some null values in the results, the query has filtered any systems that are null:
row
Name dallas
Type null
IP Address 10.10.10.10
last_seen 2008-04-05T17:36:19.0000000Z
row
Name null
Type null
IP Address
ip_address 10.20.20.20
ip_address 10.30.30.30
last_seen 2008-04-05T17:39:48.0000000Z
row
Name cuernavaca
Type null
IP Address 10.40.40.40
last_seen 2008-04-05T17:35:42.0000000Z
...
