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Oracle行列轉換方法彙總

函式名:wmsys.wm_concat

作用:以逗號分隔連線列的值

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和一些測試資料。

兩張表: employee,prject;屬性如下

1)employee: 員工ID號,員工名,部門

測試資料

0001    user1    IT 0002    user2    IT

2)prject:專案ID號,負責的員工ID號

測試資料

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

對應的SQL如下

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 專案個數的例子.

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

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;