Oracle 列转行函数 Listagg()


Oracle 列转行函数 Listagg()

这是一个Oracle的列转行函数：LISTAGG()

先看示例代码：

Sql代码







with temp as(
select 'China' nation ,'Guangzhou' city from dual union all
select 'China' nation ,'Shanghai' city from dual union all
select 'China' nation ,'Beijing' city from dual union all
select 'USA' nation ,'New York' city from dual union all
select 'USA' nation ,'Bostom' city from dual union all
select 'Japan' nation ,'Tokyo' city from dual
)
select nation,listagg(city,',') within GROUP (order by city)
from temp
group by nation

with temp as(
select 'China' nation ,'Guangzhou' city from dual union all
select 'China' nation ,'Shanghai' city from dual union all
select 'China' nation ,'Beijing' city from dual union all
select 'USA' nation ,'New York' city from dual union all
select 'USA' nation ,'Bostom' city from dual union all
select 'Japan' nation ,'Tokyo' city from dual
)
select nation,listagg(city,',') within GROUP (order by city)
from temp
group by nation

这是最基础的用法：

LISTAGG(XXX,XXX) WITHIN GROUP( ORDER BY XXX)

用法就像聚合函数一样，通过Group by语句，把每个Group的一个字段，拼接起来。

非常方便。

同样是聚合函数，还有一个高级用法：

就是over(partition by XXX)

也就是说，在你不实用Group by语句时候，也可以使用LISTAGG函数：

Sql代码







with temp as(
select 500 population, 'China' nation ,'Guangzhou' city from dual union all
select 1500 population, 'China' nation ,'Shanghai' city from dual union all
select 500 population, 'China' nation ,'Beijing' city from dual union all
select 1000 population, 'USA' nation ,'New York' city from dual union all
select 500 population, 'USA' nation ,'Bostom' city from dual union all
select 500 population, 'Japan' nation ,'Tokyo' city from dual
)
select population,
nation,
city,
listagg(city,',') within GROUP (order by city) over (partition by nation) rank
from temp

with temp as(
select 500 population, 'China' nation ,'Guangzhou' city from dual union all
select 1500 population, 'China' nation ,'Shanghai' city from dual union all
select 500 population, 'China' nation ,'Beijing' city from dual union all
select 1000 population, 'USA' nation ,'New York' city from dual union all
select 500 population, 'USA' nation ,'Bostom' city from dual union all
select 500 population, 'Japan' nation ,'Tokyo' city from dual
)
select population,
nation,
city,
listagg(city,',') within GROUP (order by city) over (partition by nation) rank
from temp

总结：LISTAGG()把它当作SUM()函数来使用就可以了。

listagg

在oracle 11g release 2 版本中新增的listagg函数，listagg是一个实现字符串聚合的oracle内建函数;

listagg(column,'分隔符') within group (order by column) over(partition by column)

分隔符可以为空，

order by必选项，可以order by null

(1)select status, listagg(risk_id, ',') within group (order by risk_id) from rp_risk group by status;

以status分组，将risk_id全部合并显示在一行

(2)与许多的聚合函数类似，listagg通过加上over()子句可以实现分析功能

select risk_id, status, listagg(risk_id, ',') within group (order by risk_id) over(partition by status) from rp_risk;

选出与当前risk_id在同一个部门的所有risk_id并合并字符串

(3)listagg聚合的结果列大小限制在varchar2类型的最大值内（比如4000);

(4)合并字符串也可以用wm_concat(column_name),所有版本的oracle都可以用这个函数

　listagg()是oracle 11g release 2才有；

(5)参考链接
http://xpchild.blog.163.com/blog/static/10180985920108485721969/
Sql代码







--listagg(合并多行的值为字符串，只用一列来显示)
select status, count(*), listagg(risk_id, ',') within group (order by risk_id) from rp_risk group by status;
select risk_id, status, listagg(risk_id, ',') within group (order by risk_id) over(partition by status) from rp_risk;
select risk.risk_id, listagg(officer.last_name || ',' || officer.first_name, '; ') within group(order by null) from rp_risk risk, rp_risk_area_ref re, rp_risk_area area, rp_risk_officer officer
where risk.risk_id = re.risk_id
and re.risk_area_id = area.risk_area_id(+)
and area.risk_officer_id = officer.risk_officer_id(+)
group by risk.risk_id;

--pivot(行专列，将多行的值改为多列显示)(for in的那个column,是某个列的值，也就是将某个列的值作为新的列的column,这个column下边的值好像只能来自一列)
select * from
(select risk.risk_id, re.risk_area_order, officer.last_name || ',' || officer.first_name fullname
from rp_risk risk, rp_risk_area_ref re, rp_risk_area area, rp_risk_officer officer
where risk.risk_id = re.risk_id
and re.risk_area_id = area.risk_area_id(+)
and area.risk_officer_id = officer.risk_officer_id(+) order by risk.risk_id desc, re.risk_area_order)
pivot(max(fullname) for risk_area_order in (1 primaryOfficer, 2 addtionalOffcier1, 3 addtionalOffcier2)) order by risk_id desc;

--decode(行专列，将多行的值改为多列显示)(decode的那个column,是某个列的值，也就是将某个列的值作为新的列的column,MAX聚集函数也可以用sum、min、avg等其他聚集函数替代)
select risk_id,
--max(decode(risk_area_order, 1, fullname)) primaryOfficer,
--max(decode(risk_area_order, 2, fullname)) addtionalOffcier1,
--max(decode(risk_area_order, 3, fullname)) addtionalOffcier1
min(decode(risk_area_order, 1, fullname)) primaryOfficer,
min(decode(risk_area_order, 2, fullname)) addtionalOffcier1,
min(decode(risk_area_order, 3, fullname)) addtionalOffcier1
from
(select risk.risk_id, re.risk_area_order, officer.last_name || ',' || officer.first_name fullname from rp_risk risk, rp_risk_area_ref re, rp_risk_area area, rp_risk_officer officer
where risk.risk_id = re.risk_id
and re.risk_area_id = area.risk_area_id(+)
and area.risk_officer_id = officer.risk_officer_id(+) order by risk.risk_id, re.risk_area_order)
group by risk_id order by risk_id;