Composite primary key duplicate records - Issue In PostgreSQL But not in Oracle

Hi Experts,

We are migrating Oracle to PostgreSQL and facing a challenge related to constrains.

In Oracle database there are lot of table consists of composite primary key which having duplicate records.

Example

• Oracle  table : --CONSTRAINT "TTT_PRX" PRIMARY KEY ("COL1", "COL2") – UNIQUE à Here in Oracle there is no issue

• In PostgreSQL if I want to add the constraint post migration it throws error as duplicate record for COL1 (which is a number) as per business need, COL2 is date which is unique always.

alter table table_name add constraint ttt_prx unique(COL1, COL2);

Is there a way to handle this in PostgreSQL?

Thanks