因为union all的每个部分可能相同,但是如果每个部分都去执行一遍的话,则成本太高,所以可以使用with as短语,则只要执行一遍即可。如果with as短语所定义的表名被调用两次以上,则优化器会自动将with as短语所获取的数据放入一个temp表里,如果只是被调用一次,则不会。而提示materialize则是强制将with as短语里的数
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), … 1 2 3 4 5 6 7 8 9 --相当于建了个e临时表 with e as (select * from scott.emp ...
一、with as with..as相当于一张中间表,可以简单理解为sql片段。 With查询语句不是以select开始的,而是以“WITH”关键字开头。 可认为在真正进行查询之前预先构造了一个临时表,之后便可多次使用它做进一步的分析和处理。 withtmpas(select*fromPersons )select*fromtmp; with as 的好处: 1、增加了sql的易读性,...
3,with as短语,也叫做子查询部分(subquery factoring),可以让你做很多事情,定义一个sql片断,该sql片断会被整个sql语句所用到。 语法: 复制 --针对一个别名withtmpas(select*fromtb_name)--针对多个别名withtmpas(select*fromtb_name),tmp2as(select*fromtb_name2),tmp3as(select*fromtb_na...
with as优点 增加了sql的易读性,如果构造了多个子查询,结构会更清晰; 更重要的是:“一次分析,多次使用”,这也是为什么会提供性能的地方,达到了“少读”的目标 with as语法 –针对一个别名 with tmp as (select * from tb_name) –针对多个别名
51CTO博客已为您找到关于oracle with tmp as的相关内容,包含IT学习相关文档代码介绍、相关教程视频课程,以及oracle with tmp as问答内容。更多oracle with tmp as相关解答可以来51CTO博客参与分享和学习,帮助广大IT技术人实现成长和进步。
3.with的使用 WITH TMP1 AS ( SELECT 1 AS A, 2 AS B FROM DUAL UNION SELECT 1 AS A, 3 AS B FROM DUAL UNION SELECT 1 AS A, 4 AS B FROM DUAL ), TMP2 AS ( SELECT 1 AS A, 2 AS B FROM DUAL UNION SELECT 1 AS A, 3 AS B FROM DUAL UNION SELECT 2 AS A, 4 AS B FROM...
WITHpAS(SELECTdeptno,job,salFROMemp),tmpAS(SELECT*FROMppivot(SUM(sal)FORjobIN('MANAGER'ASs_MANAGER,'ANALYST'ASs_ANALYST,'CLERK'ASs_CLERK,'PRESIDENT'ASs_PRESIDENT,'SALESMAN'ASs_SALESMAN)))SELECTdeptno,nvl(s_MANAGER,0)s_MANAGER,nvl(s_ANALYST,0)s_ANALYST,nvl(s_CLERK,0)s_CLERK,nvl(s_PRESID...
Oracle WIHT AS 用法 2014-05-21 11:06 −1、with table as 相当于建个临时表(用于一个语句中某些中间结果放在临时表空间的SQL语句),Oracle 9i 新增WITH语法,可以将查询中的子查询命名,放到SELECT语句的最前面。语法就是with tempname as (select ...)select ...例子:with... ㄓ...
su - root /tmp/CVU_11.2.0.0.2_oracle/runfixup.sh 13. 返回Execute Fixup Scripts 窗口,单击 OK。 14. 在Summary 窗口中,单击 Finish。 15. 将显示进度窗口。 16. 软件安装之后,Database Configuration Assistant 将开始运行并创建您的数据库。 17. 数据库创建成功。单击 Close。 18. 您需要以...