问题：ORA-00918:未明确定义列
eg.
select
name, name
from a left
join b on a.flag = b.flag
原因：列名重复了(select后面跟了两个 name)
解决办法：每个列名，都加上其所在表的表名作为前缀
eg.
select a.name, b.name
from a left
join b on a.flag = b.flag
问题：ORA-00918:未明确定义列
eg.
select
name, name
from a left
join b on a.flag = b.flag
原因：列名重复了(select后面跟了两个 name)
解决办法：每个列名，都加上其所在表的表名作为前缀
eg.
select a.name, b.name
from a left
join b on a.flag = b.flag