Add primary key to existing table

I have an existing table called Persion. In this table I have 5 columns:

• persionId
• Pname
• PMid
• Pdescription
• Pamt

When I created this table, I set PersionId and Pname as the primary key.

I now want to include one more column in the primary key - PMID. How can I write an ALTER statement to do this? (I already have 1000 records in the table)

drop constraint and recreate it

alter table Persion drop CONSTRAINT <constraint_name>

alter table Persion add primary key (persionId,Pname,PMID)

edit:

you can find the constraint name by using the query below:

select OBJECT_NAME(OBJECT_ID) AS NameofConstraint
FROM sys.objects
where OBJECT_NAME(parent_object_id)='Persion'
and type_desc LIKE '%CONSTRAINT'

I think something like this should work

-- drop current primary key constraint
ALTER TABLE dbo.persion 
DROP CONSTRAINT PK_persionId;
GO

-- add new auto incremented field
ALTER TABLE dbo.persion 
ADD pmid BIGINT IDENTITY;
GO

-- create new primary key constraint
ALTER TABLE dbo.persion 
ADD CONSTRAINT PK_persionId PRIMARY KEY NONCLUSTERED (pmid, persionId);
GO