Aggregate query scenario while updating field to multi field type

We have below 2 indexes
-> index1 has field HOST
-> index2 has 2 fields HOST & HOST.raw

I want to perform aggregate query on HOST such that for index1 it should consider field HOST and for index2 it should consider field HOST.raw
Basically if HOST.raw is present then consider it else take HOST

Presently we are using below query which considers only HOST field.(not HOST.raw if available in index)
"aggregations" : {
"HOST" : {
"terms" : {
"field" : "HOST",
"size" : 500,
"order" : {
"_count" : "asc"

Is there any way I can accomodate my requirement by modifying query ?

It is only possible with a scripted terms aggregation. That will give you poor performance though.

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