oracle中 with as, decode ,where 1=1等的用法 |
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1.with as
转自：https://www.cnblogs.com/linjiqin/archive/2013/06/24/3152667.html 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), … –相当于建了个e临时表 with e as (select * from scott.emp e where e.empno=7499) select * from e;–相当于建了e、d临时表 with e as (select * from scott.emp), d as (select * from scott.dept) select * from e, d where e.deptno = d.deptno;其实就是把一大堆重复用到的sql语句放在with as里面，取一个别名，后面的查询就可以用它，这样对于大批量的sql语句起到一个优化的作用，而且清楚明了。 向一张表插入数据的with as用法 insert into table2 with s1 as (select rownum c1 from dual connect by rownum |
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