java.sql.SQLException: ORA-02292: 违反完整约束条件 (JAVAEE.T_MC_NMAXID_FK) - 已找到子记录

源代码：
--删除商品类别的储存过程
create or replace procedure deleteParentTydeTrigger(nid in varchar2) is
begin

delete from t_mc t where t.nmaxid = nid;
delete from t_mc_type t where t.pid = nid;
delete from t_mc_type t where t.nid= nid;
end deleteParentTydeTrigger;
/

参数名改为其他的，如aa ，就ok了、nid为字段名，原因？