SQL SERVER ALTER THE TABLE

WHAT IS THE ERROR IN FOLLOWING CODE

ALTER TABLE Item_Master_Sample.DBO.Table_2_Master ADD CONSTRAINT PK_ITEM_CODE PRIMARY KEY CLUSTERED (ITEM_CODE ASC) ON [PRIMARY]

HERE

Item_Master_Sample-Database name

Table_2_Master-table name

ITEM_CODE-table item which i want it to be primary key

How i resole this solution ...pls anyone....?