一、查询某表中某列值相同的记录：
select * from t_acct_map where acct_id in (
select acct_id from t_acct_map group by acct_id having count(*)>1
)
order by acct_id
二、自连接
当表中的某一个字段与这个表中另外字段的相关时，才可能用到
select bi.brh_nm||'_'||bi.brh_id||'_'||bi.sup_brh_id sub,' 的父公司 ',b.brh_nm||b.brh_id sup
from t_brh_info b ,t_brh_info bi
where b.brh_id=bi.sup_brh_id
union select brh_nm||'_'||brh_id sub,' 的父公司 ', brh_nm||'_'||sup_brh_id sup from t_brh_info where sup_brh_id is NULL
order by sup desc
;
