函數名:wmsys.wm_concat
作用:以逗號分隔連接列的值
oracle 10g引入。使用時直接用wm_concat也可以。
以下介紹一些實際使用的狀況。介紹實際Case前先建立一個測試table和一些測試數據。
兩張表: employee,prject;屬性如下
1)employee: 員工ID號,員工名,部門
測試數據
0001 user1 IT
0002 user2 IT
2)prject:項目ID號,負責的員工ID號
測試數據
PN001 0001
PN002 0001
PN003 0001
PN004 0001
PN010 0002
PN011 0002
對應的SQL如下
[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: 列轉換行。 以一行顯示所有員工的名字
select wmsys.wm_concat(NAME) from employee;
結果: user1,user2
Case 2: join 兩張table , 計算員工負責的 項目個數的例子.
[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;
結果:
0001 IT 4
0002 IT 2
此Case如果使用Count替代的話也可以,而且寫法更簡單,但是table很複雜的時候使用count不能達成時,可以考慮這個方式, 此處附上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;