How to dedup non-overlapping fields in separate sources?

[yuanliu]

I have two different sources with different fields.  Let's call them sourcetypeA and sourcetypeB.  Some fields that I wanted to dedup do not overlap.  Let's say sfieldA only exists in sourcetypeA, sfieldB only exists in sourcetypeB.  My intention is to have a single search (without append) to return events from both sources that contain unique sfieldA in sourcetypeA and unique sfieldB in sourcetypeB.

I was initially surprised that the following returned no event:

sourcetype = sourcetypeA OR sourcetype = sourcetype B
| dedup sfieldA sfieldB

Then, I realized that this is to ask for dedup on nonexistent keys.  My question is, then: Is there a syntax to express my intent?

[richgalloway · Accepted solution]

The method requires creating a common field.

sourcetype = sourcetypeA OR sourcetype = sourcetype B
| eval sfield = coalesce(sfieldA, sfieldB)
| dedup sfield

The coalesce function sets sfield to whichever field of sfieldA and sfieldB exists in the current event.