ORACLE以逗号分隔链接列的值 函数名：wmsys.wm_concat

函数名：wmsys.wm_concat

做用：以逗号分隔链接列的值

oracle 10g引入。使用时直接用wm_concat也能够。

如下介绍一些实际使用的情况。介绍实际Case前先创建一个测试table和一些测试数据。

两张表： employee，prject；属性以下

1)employee： 员工ID号，员工名，部门

测试数据

0001    user1    IT
0002    user2    IT

2)prject：项目ID号，负责的员工ID号

测试数据

PN001    0001
PN002    0001
PN003    0001
PN004    0001
PN010    0002
PN011    0002

对应的SQL以下

[sql] view plaincopy

create table employee
(
  ID varchar(4) NOT NULL PRIMARY KEY,
  NAME varchar(20),
  DEPT varchar(20)
);
create table prject
(
   PROJECTID varchar(5) NOT NULL PRIMARY KEY,
   OWNERID varchar(20)
);

INSERT INTO employee(ID,NAME,DEPT) Values(‘0001’,‘user1’,‘IT’);
INSERT INTO employee(ID,NAME,DEPT) Values(‘0002’,‘user2’,‘IT’);

INSERT INTO prject(PROJECTID,OWNERID) Values(‘PN001’,‘0001’);
INSERT INTO prject(PROJECTID,OWNERID) Values(‘PN002’,‘0001’);
INSERT INTO prject(PROJECTID,OWNERID) Values(‘PN003’,‘0001’);
INSERT INTO prject(PROJECTID,OWNERID) Values(‘PN004’,‘0001’);
INSERT INTO prject(PROJECTID,OWNERID) Values(‘PN010’,‘0002’);
INSERT INTO prject(PROJECTID,OWNERID) Values(‘PN011’,‘0002’);

 

Case 1: 列转换行。 以一行显示全部员工的名字

     select wmsys.wm_concat(NAME) from employee;

     结果： user1,user2

Case 2: join 两张table , 计算员工负责的 项目个数的例子.

[sql] view plaincopy

select t1.ID,t1.DEPT,t2.pcount from
(select ID,NAME,DEPT from employee) t1 left outer join
(select OWNERID,trunc(length(replace(wm_concat(PROJECTID),‘,’,”))/5) as pcount from prject group by OWNERID) t2 on t1.ID = t2.OWNERID;

结果：

 

0001    IT    4
0002    IT    2

此Case若是使用Count替代的话也能够，并且写法更简单，可是table很复杂的时候使用count不能达成时，能够考虑这个方式， 此处附上count方式

[sql] view plaincopy

select t1.ID,t1.DEPT,t2.pcount from
(select ID,NAME,DEPT from employee) t1 left outer join
(select OWNERID,count(PROJECTID) as pcount from prject group by OWNERID) t2 on t1.ID = t2.OWNERID;