问题
Is it possible to do upsert in Postgres 9.5 when conflict happens on one of 2 columns in a table.? Basically I have 2 columns and if either column throws unique constraint violation, then I would like to perform update operation.
回答1:
Yes, and this behaviour is default. Any unique constraint violation constitutes a conflict and then the UPDATE is performed if ON CONFLICT DO UPDATE is specified. The INSERT statement can have only a single ON CONFLICT clause, but the conflict_target of that clause can specify multiple column names each of which must have an index, such as a UNIQUE constraint. You are, however, limited to a single conflict_action and you will not have information on which constraint caused the conflict when processing that action. If you need that kind of information, or specific action depending on the constraint violation, you should write a trigger function but then you lose the all-important atomicity of the INSERT ... ON CONFLICT DO ... statement.
回答2:
I think in Postgres 9.5 ON CONFLICT can have only one constraint or multiple column names but on that multiple columns must have combine one index
来源：https://stackoverflow.com/questions/35031934/how-to-upsert-in-postgres-on-conflict-on-one-of-2-columns