测试oracle with as

http://www.cnblogs.com/booolee/archive/2009/09/15/1566827.html

测试oracle with as

为了简化SQL语句，可以将语句分成若干个视图来操作，但是创建的试图将会作为对象保存在数据库中，但经常有一些语句只是临时使用，所以在sql-99规范中有了with as 语句，该语句实质上就是创建临时视图，来帮助你简化语句并使语句结构更清晰更容易阅读。

 

下面的测试中会用到3张表，courseresults（课程-学生-成绩表）、courses（课程表）、students(学生表)，先给出建表语句：

create table COURSERESULTS
(
  CID   NUMBER,
  SID   NUMBER,
  SCORE FLOAT not null
)

create table COURSES
(
  CID     NUMBER not null,
  CNAME   VARCHAR2(100) not null,
  TID     NUMBER,
  CREDITS NUMBER not null
)

create table STUDENTS
(
  SID       NUMBER not null,
  SNAME     VARCHAR2(50) not null,
  SEX       CHAR(1),
  BIRTHDATE DATE,
  EMAIL     VARCHAR2(50)
)

 

例1：获取student表全部数据

with s as

(select * from students)

select * from s;

 

例2：获取小于平均成绩的学生学号和成绩

with c as
(select avg(score) as value from courseresults)
select sid,score from courseresults,c where score>c.value;

 

例3：获取课程平均成绩大于85分的男生的学号

with
s1 as
(select sid from courseresults group by sid having avg(score)>85),
s2 as
(select sid from students where sex='m')
select * from s1 intersect select * from s2;

 

结论：使用with as语句的确可以使复杂的SQL语句具有更清晰的结构。

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====me test

插入时:

insert into gjtable

with
s1 as
(select sid from courseresults group by sid having avg(score)>85),
s2 as
(select sid from students where sex='m')
select * from s1 intersect select * from s2;