Question

I have a 5GB that has 3 columns as a unique (non-clustered) index. I want to promote these three to be the new primary key (clustered). Should I drop this index before change the PK?

Also I am planning on dropping this index after I change the PK.

The types of the three fields are

field1: int
field2: int
field3: char(7) 

Update:
Change the word promoting to dropping and setting

Answer 1

You cannot promote an existing index to primary key (or anything else).

You’ll have to drop the unique index first, then create a new primary key constraint on those three columns (which will automatically create the primary key index)