行转列

一、case when then else end 用法：

CASE sex
WHEN '1' THEN '男'
WHEN '2' THEN '女'
ELSE '其他' END
--Case搜索函数
CASE WHEN sex = '1' THEN '男'
WHEN sex = '2' THEN '女'
ELSE '其他' END

二、with as 用法：
WITH AS的含义
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。有的时候，是为了让SQL语句的可读性更高些，

也有可能是在UNION ALL的不同部分，作为提供数据的部分。
特别对于UNION ALL比较有用。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短语里的数据放入一个

全局临时表里。很多查询通过这种方法都可以提高速度。

with as语法
1.–针对一个别名

with tmp as (select * from tb_name)

　　

2.–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),
…

　　

3.--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;

　　

4.--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。

5.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 <= 10),
s2 as (select rownum c2 from dual connect by rownum <= 10)
select a.c1, b.c2 from s1 a, s2 b where...;

select s1.sid, s2.sid from s1 ,s2需要有关联条件，不然结果会是笛卡尔积。
with as 相当于虚拟视图。

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。有的时候，是为了让sql语句的可读性更高些，也有可能是在union all的不同部分，作为提供数据的部分。
　　
特别对于union all比较有用。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短语里的数据放入一个全局临时表里。很多查询通过这种方法都可以提高速度。

with
sql1 as (select to_char(a) s_name from test_tempa),
sql2 as (select to_char(b) s_name from test_tempb where not exists (select s_name from sql1 where rownum=1))
select * from sql1
union all
select * from sql2
union all
select 'no records' from dual
where not exists (select s_name from sql1 where rownum=1)
and not exists (select s_name from sql2 where rownum=1);

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 MIXDATA AS (
SELECT '110' AS OWNER
       ,SUBSTR(WA1_WDATE,1,6) DATE
       ,SUM(WA1_REQTY) REQTY
  FROM KTGW.GWA1010
 WHERE WA1_WDATE BETWEEN '20170101' AND '20170731'
   AND RIGHT(TRIM(WA1_ITNBR),1) = 'F'
 GROUP BY SUBSTR(WA1_WDATE,1,6)
),
BUCU_DATA AS (
SELECT WA1_OWNER OWNER
       ,SUBSTR(WA1_WDATE,1,6) DATE
       ,SUM(WA1_REQTY) REQTY
  FROM KTGW.GWA0010
 WHERE WA1_WDATE BETWEEN '20170101' AND '20170731'
 GROUP BY WA1_OWNER,SUBSTR(WA1_WDATE,1,6)
),
HALFDATE AS(
SELECT WA5_OWNER OWNER
         ,SUBSTR(WA5_WDATE,1,6) DATE
         ,SUM(WA5_REQTY) REQTY
  FROM KTGW.GWA2050
 WHERE WA5_WDATE BETWEEN '20170101' AND '20170731'
      AND  WA5_OWNER<>'' 
 GROUP BY SUBSTR(WA5_WDATE,1,6),WA5_OWNER
 ORDER BY SUBSTR(WA5_WDATE,1,6),WA5_OWNER
),
ALLDATA AS (
SELECT * FROM BUCU_DATA
UNION ALL
SELECT * FROM MIXDATA
UNION ALL 
SELECT * FROM HALFDATE
)

SELECT OWNER
       ,SUM(CASE WHEN OWNER = '110' AND SUBSTR(DATE,5,2) = '01' THEN REQTY
                 WHEN OWNER = '120' AND SUBSTR(DATE,5,2) = '01' THEN REQTY
                 WHEN OWNER = '130' AND SUBSTR(DATE,5,2) = '01' THEN REQTY
                 WHEN OWNER = '140' AND SUBSTR(DATE,5,2) = '01' THEN REQTY
                 WHEN OWNER = '150' AND SUBSTR(DATE,5,2) = '01' THEN REQTY
                 WHEN OWNER = '160' AND SUBSTR(DATE,5,2) = '01' THEN REQTY
                 WHEN OWNER = '170' AND SUBSTR(DATE,5,2) = '01' THEN REQTY END)
 FROM ALLDATA
 GROUP BY OWNER
 ORDER BY OWNER

　　

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