prss.net
当前位置:首页 >> orAClE with As >>

orAClE with As

with as语法 –针对一个别名 with tmp as (select * from tb_name) –针对多个别名 with tmp as (select * from tb_name), tmp2 as (select * from tb_name2), tmp3 as (select * from tb_name3), 其实就是把一大堆重复用到的sql语句放在with as里...

oracle with as Oracle作为 oracle with as Oracle作为

你要问支持吗,我就回答:支持 顺便告诉你怎么用: with TT as( --模拟生一个20行的数据 SELECT LEVEL AS lv FROM DUAL CONNECT BY LEVEL < 20 ) select lv from TT WHERE lv > 10 AND lv < 15

with as语法 –针对一个别名 with tmp as (select * from tb_name) –针对多个别名 with tmp as (select * from tb_name), tmp2 as (select * from tb_name2), tmp3 as (select * from tb_name3), 其实就是把一大堆重复用到的sql语句放在with as里

当然可以,With可以认为是SQL一句话中的定义部分 例如 with 子查询1 as (select XXX as 字段1,字段2.。。。。。。。) select 子查询1.字段1 表1.xxx from 子查询1,表1.。。。。。。。。 重要的是,上面的SQL是一句话哦! with可以认为SQL临时...

可以的, test: with sql1 as (select * from dba_objects), sql2 as (select * from sql1 where rownum

可以使用的,with相当于建了个临时表。但是只能结合游标使用。 比如 procedure TEST(OUT_RESULT out MYTYPE) is begin open cur for with emp as (select * from scott.emp e where e.empno=7499) select * from e;

如果select的结果有多处地方会用到,那么with as会把select的结果缓存起来,不用每次都select from,少写代买,而且效率也比较高。

单纯的执行这一次没有什么不同,效率差不多 如果需要反复引用结果就用WITH。with as 主要是对于语句中多次引用sql结果集(中间集),一次生成,多次引用,执行效率非常高

12345with temp as (select /*+hint1*/ ******)select /*+hint2*/* from temp;--hint1作用于temp内结果集,hint2作用域temp外

网站首页 | 网站地图
All rights reserved Powered by www.prss.net
copyright ©right 2010-2021。
内容来自网络,如有侵犯请联系客服。zhit325@qq.com