–根据模式名和表名查询出表的主键列，将实例中的DEM换成对应的模式名，ADMIN_USER换成对应的表名即可

SELECT
        A.OWNER     ,
        A.TABLE_NAME,
        WM_CONCAT(B.COLUMN_NAME) PK_COLUMNS
FROM
        ALL_CONSTRAINTS A,
        ALL_CONS_COLUMNS B
where
        A.CONSTRAINT_type='P'
    AND A.OWNER          ='DEM'
    AND A.TABLE_NAME     ='ADMIN_USER'
    AND B.OWNER   =A.OWNER
    AND A.TABLE_NAME     =B.TABLE_NAME
GROUP BY
        A.OWNER,
        A.TABLE_NAME;