多行转字符串
这个比较简单,用||或concat函数可以实现
- 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
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
- 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
- select wm_concat(name) name from test;

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

效果3: 按ID分组合并name
- select id,wm_concat(name) name from test group by id;
sql语句等同于下面的sql语句
- -------- 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;
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
- /** 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
- select * from user_tab_columns

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./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。
- 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)
- select name, sum(nums) nums from demo group by name

行转列查询
- 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
- ------ 多项子查询
- 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');
-
- ------ decode 函数利用
- select sum(decode(name,'苹果',nums)) 苹果, sum(decode(name,'橘子',nums)) 橘子,
- sum(decode(name,'葡萄',nums)) 葡萄, sum(decode(name,'芒果',nums)) 芒果 from demo
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
- 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
- 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
- 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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