Here you go:
SELECT d.IPAddress AS "DISCOVERED IP ADDRESS", d.SysName AS "DISCOVERED DEVICE" FROM DiscoveredNodes d JOIN Nodes n ON d.IPAddress=n.IP_Address WHERE n.IP_Address is NULL AND d.IgnoredNodeID IS NULL
You can use that to make a Custom SQL report in either the legacy Report Writer or the new Web-based.
Basic Function:
Look at all of your discovered nodes that are not in the ignored list. Compare that data against all the current nodes that are already in SolarWinds. If the IP_Address field in the Nodes table is NULL, then the node has not been imported yet.
If you have multiple discovery profiles running, you can further edit/enhance this report by finding the ProfileID from the DiscoveryProfiles table and then adding a statement at the end of your report (this can be helpful if you are trying to report on regions/teams/etc that have their own discoveries running)
SELECT ProfileID, Name, Description FROM DiscoveryProfiles
AND d.ProfileID = 'INSERT # HERE'
ZackM