最近在研究connect by的一些基本知识和运行原理,看到有一个sql,会显示connect by操作内存不足,不是很懂这句sql是怎么个逻辑。
with a as (
select 5 as n from dual
union all
select 10 from dual
union all
select 15 from dual
union all
select 20 from dual
)
select * from a where rownum=1 connect by rownum<6;
如果没有where条件可以理解,加了where就不明白,
有没有大神可以解释一下?
with a as (
select 5 as n from dual
union all
select 10 from dual
union all
select 15 from dual
union all
select 20 from dual
)
select * from a where rownum=1 connect by rownum<6;
如果没有where条件可以理解,加了where就不明白,
有没有大神可以解释一下?
是因为每次循环都是rownum=1,所以死循环了嘛?
with a as (
select 5 as n from dual
union all
select 10 from dual
union all
select 15 from dual
union all
select 20 from dual
)
select * from a where rownum<4 connect by level<6;
这一句的where又是筛选最后的结果的。
在这里面,where语句到底应该是在每一次循环作用,还是在最后才作用?
select 5 as n from dual
union all
select 10 from dual
union all
select 15 from dual
union all
select 20 from dual
)
select * from a where rownum<6 connect by rownum=1;