ORA-01722:无效数字

SELECT * FROM (select a.nursing_unit_code,
b.name nursingName,
a.ward_code,
c.name warName,
c.parent_id,
a.hospital_area_code
from pts.pts_dept_ward_nurse_mapping a,
bds.bds_organization b,
bds.bds_organization c
where a.nursing_unit_code = b.code
and a.ward_code = c.code) abc LEFT JOIN bds.bds_organization d ON abc.parent_id = d.code;

code是VARCHAR2(32)类型，而parentId是NUMBER(10)类型