Can I add a UNIQUE constraint to a PostgreSQL table, after it's already created?

Question

I have the following table:

 tickername | tickerbbname  | tickertype
------------+---------------+------------
 USDZAR     | USDZAR Curncy | C
 EURCZK     |          


        

Answer 1

Yes, you can add a UNIQUE constraint after the fact. However, if you have non-unique entries in your table Postgres will complain about it until you correct them.