db2构建临时结果集

一

values  ('1',2,3)   为一行   ‘1’   2    3   行数据类型可以不同  values  ('1',2,3),('f',5,6) 为两行

（values  1,2,3）   为一列

1

2

3

所以数据类型必须一样，不然报错

二  with做临时表，with还可以递归查询

二.1 with可以和select语句组合做临时表

CREATE TABLE USER
(
NAME VARCHAR(20) NOT NULL,--姓名
DEGREE INTEGER NOT NULL,--学历(1、专科 2、本科 3、硕士 4、博士)
STARTWORKDATE date NOT NULL,--入职时间
SALARY1 FLOAT NOT NULL,--基本工资
SALARY2 FLOAT NOT NULL--奖金
); 

假设现在让你查询一下那些 1、学历是硕士或博士  2、学历相同，入职年份也相同，但是工资（基本工资+奖金）却比相同条件员工的平均工资低的员工。（哈哈，可能是要涨工资），不知道你听明白问题没有？该怎么查询呢？

对比两种方式：

a

WITH TEMP1(NAME,DEGREE,WORDDATE,SALARY) AS
(
SELECT NAME,DEGREE,YEAR(STARTWORKDATE) AS WORDDATE, SALARY1+SALARY2 AS SALARY FROM USER WHERE DEGREE IN (3,4)
),
TEMP2 (DEGREE,WORDDATE,AVG_SALARY) AS
(
SELECT DEGREE,YEAR(STARTWORKDATE) AS WORDDATE, AVG(SALARY1+SALARY2) AS AVG_SALARY
FROM USER WHERE DEGREE IN (3,4)
GROUP BY DEGREE,YEAR(STARTWORKDATE)
)
SELECT NAME FROM TEMP1, TEMP2 WHERE
TEMP1.DEGREE=TEMP2.DEGREE
AND TEMP1.WORDDATE=TEMP2.WORDDATE
AND SALARY<AVG_SALARY;  

b

WITH TEMP1(NAME,DEGREE,WORDDATE,SALARY) AS
(
SELECT NAME,DEGREE,YEAR(STARTWORKDATE) AS WORDDATE, SALARY1+SALARY2 AS SALARY FROM USER WHERE DEGREE IN (3,4)
),
TEMP2 (DEGREE,WORDDATE,AVG_SALARY) AS
(
SELECT DEGREE,WORDDATE, AVG(SALARY) AS AVG_SALARY
FROM TEMP1
GROUP BY DEGREE,WORDDATE
)
SELECT NAME FROM TEMP1, TEMP2 WHERE
TEMP1.DEGREE=TEMP2.DEGREE
AND TEMP1.WORDDATE=TEMP2.WORDDATE
AND SALARY<AVG_SALARY;  

递归用法:

论坛首页
--数据库开发
----DB2
------DB2 文章1
--------DB2 文章1 的评论1
--------DB2 文章1 的评论2
------DB2 文章2
----Oracle
--Java技术  

CREATE TABLE BBS
(
PARENTID INTEGER NOT NULL,
ID INTEGER NOT NULL,
NAME VARCHAR(200) NOT NULL---板块、文章、评论等。
);
insert into bbs (PARENTID,ID,NAME) values
(0,0,'论坛首页'),
(0,1,'数据库开发'),
(1,11,'DB2'),
(11,111,'DB2 文章1'),
(111,1111,'DB2 文章1 的评论1'),
(111,1112,'DB2 文章1 的评论2'),
(11,112,'DB2 文章2'),
(1,12,'Oracle'),
(0,2,'Java技术'); 

查询一下DB2的所有文章及评论，怎么办？

WITH TEMP(PARENTID,ID,NAME) AS
(
SELECT PARENTID,ID,NAME FROM BBS WHERE NAME='DB2'---语句1
UNION ALL---语句2
SELECT B.PARENTID,B.ID,B.NAME FROM BBS AS B, TEMP AS T WHERE B.PARENTID=T.ID---语句3
)
SELECT NAME FROM TEMP;---语句4