使用 start with a= ‘起始ID‘ connect by prior a= b
a为子项，b为父项。
select F_CA_CODE,F_CA_PARENTCODE,LEVEL from RGT_UNIT start with F_CA_CODE = ‘0‘ connect by prior F_CA_CODE = F_CA_PARENTCODE
查询结果：
其中LEVEL为oracle内置函数
如果加入查询条件需要在start with前面加入：
select F_CA_CODE,F_CA_PARENTCODE,LEVEL from RGT_UNIT where LEVEL=3 start with F_CA_CODE = ‘0‘ connect by prior F_CA_CODE = F_CA_PARENTCODE
查询结果：
http://www.cnblogs.com/no27/p/4221650.html
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http://www.cnblogs.com/xfrog/archive/2010/10/10/1847462.html
原文：http://www.cnblogs.com/lsyyx/p/4221701.html