如何在Oracle中使用WITHIN GROUP的LISTAGG函数将列转换为行？

1.基础用法：LISTAGG(XXX,XXX) WITHIN GROUP( ORDER BY XXX)，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

LISTAGG()其实可以把它当作SUM()函数来使用或者理解

（1）示例代码： 

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)  AS CITIES

FROM TEMP 

GROUP BY NATION

（2）示例代码:

查询部门为20的员工列表:SELECT t.DEPTNO,t.ENAME FROM SCOTT.EMP t where t.DEPTNO = '20';

使用  listagg() WITHIN GROUP ()  将多行合并成一行：

SELECT

T .DEPTNO,

LISTAGG (T .ENAME, ',') WITHIN GROUP (ORDER BY T .ENAME) NAMES

FROM SCOTT.EMP T

WHERE

T .DEPTNO = '20' GROUP BY T .DEPTNO

2.高级用法：over(partition by XXX)。在不使用Group by语句时候，也可以使用LISTAGG函数：

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