CANNOT USE ANY INDEX ON UPSERT (INSERT.....ON CONFLICT)

Hi all,

I have a problem with INSERT ... ON CONFLICT sql command.

Reading 9.6 documentation i see that ON CONFLICT command will accpets
only index_column_name or index_expression (unique composite/primary
indexes are valid too).

So, my problem is that i can't create any type of upsert-valid index .
Let me explain.

I have a table T1 containing F1, F2, F3, F4 fields.

I can insert same records in T1, *MAX TWICE*.

I can have records like (A,B,C,D),(B,A,D,C), etc.. and (A,B,C,D) AGAIN.
Any other next insert of (A,B,C,D) is not allowed (actually it is
avoided by a complex-and-slow-performance select count in before
insert/update trigger).

In this case i can't create any type of primary/unique index, like a
composite F1,F2, F3, F4 index. (correct me if i am wrong please).

So, how to use UPSERT in this case?

Best regards,

Agharta