We are mostly creating primary key on column while creating tables, But sometime we also need to have it after creating table or on existing table as per need, So i am sharing the script to add primary key on table.

We can create a primary key on table with two options like i mentioned in the code below,

-- Option #1
ALTER TABLE TableName 
ADD PRIMARY KEY (ColumnName)
GO

-- Option #2
ALTER TABLE TableName
ADD CONSTRAINT PK_TableName_ColumnName PRIMARY KEY(ColumnName)
GO

In option #1 constraint will be created with default name as per system and in option #2 constraint will be created with the same name which we have mentioned.