oracle行转列，列转行

多行转字符串
这个比较简单，用||或concat函数可以实现
SQL Code
select concat(id,username) str from app_user
select id||username str from app_user
字符串转多列
实际上就是拆分字符串的问题，可以使用 substr、instr、regexp_substr函数方式
字符串转多行
使用union all函数等方式
wm_concat函数
首先让我们来看看这个神奇的函数wm_concat(列名),该函数可以把列值以","号分隔起来,并显示成一行,接下来上例子,看看这个神奇的函数如何应用准备测试数据
SQL Code
create table test(id number,name varchar2(20));
insert into test values(1,'a');
insert into test values(1,'b');
insert into test values(1,'c');
insert into test values(2,'d');
insert into test values(2,'e');
效果1 : 行转列，默认逗号隔开
SQL Code
select wm_concat(name) name from test;

效果2: 把结果里的逗号替换成"|"
SQL Code
select replace(wm_concat(name),',','|') from test;

效果3: 按ID分组合并name

SQL Code
select id,wm_concat(name) name from test group by id;

sql语句等同于下面的sql语句:
  SQL Code
-------- 适用范围：8i,9i,10g及以后版本  （ MAX + DECODE ）
select id,
       max(decode(rn, 1, name, null)) ||
       max(decode(rn, 2, ',' || name, null)) ||
       max(decode(rn, 3, ',' || name, null)) str
  from (select id,
               name,
               row_number() over(partition by id order by name) as rn
          from test) t
group by id
order by 1;
-------- 适用范围：8i,9i,10g及以后版本（ ROW_NUMBER + LEAD ）
select id, str
  from (select id,
               row_number() over(partition by id order by name) as rn,
               name || lead(',' || name, 1) over(partition by id order by name) ||
               lead(',' || name, 2) over(partition by id order by name) ||
               lead(',' || name, 3) over(partition by id order by name) as str
          from test)
where rn = 1
order by 1;
-------- 适用范围：10g及以后版本（ MODEL ）
select id, substr(str, 2) str
  from test model return updated rows partition by(id) dimension by(row_number()
  over(partition by id order by name) as rn) measures(cast(name as varchar2(20)) as str)
  rules upsert iterate(3) until(presentv(str [ iteration_number + 2 ], 1, 0) = 0)
  (str [ 0 ] = str [ 0 ] || ',' || str [ iteration_number + 1 ])
order by 1;
-------- 适用范围：8i,9i,10g及以后版本（ MAX + DECODE ）
select t.id id, max(substr(sys_connect_by_path(t.name, ','), 2)) str
  from (select id, name, row_number() over(partition by id order by name) rn
          from test) t
start with rn = 1
connect by rn = prior rn + 1
       and id = prior id
group by t.id;

懒人扩展用法:
案例: 我要写一个视图,类似"create or replace view as select 字段1,...字段50 from tablename" ,基表有50多个字段,要是靠手工写太麻烦了,有没有什么简便的方法? 当然有了,看我如果应用wm_concat来让这个需求变简单，假设我的APP_USER表中有（id,username,password,age）4个字段。查询结果如下
SQL Code
/** 这里的表名默认区分大小写 */
select 'create or replace view as select ' || wm_concat(column_name) ||
       ' from APP_USER' sqlStr
  from user_tab_columns
where table_name = 'APP_USER';

利用系统表方式查询
SQL Code
select * from user_tab_columns
Oracle 11g 行列互换 pivot 和 unpivot 说明
在Oracle 11g中，Oracle 又增加了2个查询：pivot（行转列）和unpivot（列转行）
参考：http://blog.csdn.net/tianlesoftware/article/details/7060306、http://www.oracle.com/technetwork/cn/articles/11g-pivot-101924-zhs.html
google 一下，网上有一篇比较详细的文档：http://www.oracle-developer.net/display.php?id=506
pivot 列转行
测试数据 (id，类型名称，销售数量)，案例：根据水果的类型查询出一条数据显示出每种类型的销售数量。
SQL Code
create table demo(id int,name varchar(20),nums int); ---- 创建表
insert into demo values(1, '苹果', 1000);
insert into demo values(2, '苹果', 2000);
insert into demo values(3, '苹果', 4000);
insert into demo values(4, '橘子', 5000);
insert into demo values(5, '橘子', 3000);
insert into demo values(6, '葡萄', 3500);
insert into demo values(7, '芒果', 4200);
insert into demo values(8, '芒果', 5500);

分组查询（当然这是不符合查询一条数据的要求的）
SQL Code
select name, sum(nums) nums from demo group by name

行转列查询
SQL Code
select * from (select name, nums from demo) pivot (sum(nums) for name in ('苹果' 苹果, '橘子', '葡萄', '芒果'));

注意： pivot（聚合函数 for 列名 in（类型）），其中 in('') 中可以指定别名，in中还可以指定子查询，比如 select distinct code from customers
当然也可以不使用pivot函数，等同于下列语句，只是代码比较长，容易理解
SQL Code
select *
  from (select sum(nums) 苹果 from demo where name = '苹果'),
       (select sum(nums) 橘子 from demo where name = '橘子'),
       (select sum(nums) 葡萄 from demo where name = '葡萄'),
       (select sum(nums) 芒果 from demo where name = '芒果');
unpivot 行转列
顾名思义就是将多列转换成1列中去
案例：现在有一个水果表，记录了4个季度的销售数量，现在要将每种水果的每个季度的销售情况用多行数据展示。
创建表和数据
SQL Code
create table Fruit(id int,name varchar(20), Q1 int, Q2 int, Q3 int, Q4 int);
insert into Fruit values(1,'苹果',1000,2000,3300,5000);
insert into Fruit values(2,'橘子',3000,3000,3200,1500);
insert into Fruit values(3,'香蕉',2500,3500,2200,2500);
insert into Fruit values(4,'葡萄',1500,2500,1200,3500);
select * from Fruit

列转行查询
SQL Code
select id , name, jidu, xiaoshou from Fruit unpivot (xiaoshou for jidu in (q1, q2, q3, q4) )
注意： unpivot没有聚合函数，xiaoshou、jidu字段也是临时的变量

同样不使用unpivot也可以实现同样的效果，只是sql语句会很长，而且执行速度效率也没有前者高
SQL Code
select id, name ,'Q1' jidu, (select q1 from fruit where id=f.id) xiaoshou from Fruit f
union
select id, name ,'Q2' jidu, (select q2 from fruit where id=f.id) xiaoshou from Fruit f
union
select id, name ,'Q3' jidu, (select q3 from fruit where id=f.id) xiaoshou from Fruit f
union
select id, name ,'Q4' jidu, (select q4 from fruit where id=f.id) xiaoshou from Fruit f

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oracle行转列，列转行

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