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     | EURCZK Curncy | C

 EURPLN     | EURPLN Curncy | C

 USDBRL     | USDBRL Curncy | C

 USDTRY     | USDTRY Curncy | C

 EURHUF     | EURHUF Curncy | C

 USDRUB     | USDRUB Curncy | C

I don't want there to ever be more than one column for any given tickername/tickerbbname pair. I've already created the table and have lots of data in it (which I have already ensured meets the unique criteria). As it gets larger, though, room for error creeps in.

Is there any way to add a UNIQUE constraint at this point?

Answer 1

According to psql's inline:

\h ALTER TABLE

Also,  it's mentioned in the postgres docs(an excellent resource, plus easy to read, too) like this:

ALTER TABLE tablename ADD CONSTRAINT constraintname UNIQUE (columns);