SQL函数:wm_concat
wm_concat(column):此函数实现字段合并,可以把列值以","号分隔起来并显示成一行,实现行转列的效果。
例如:表shopping:
-----------------------------------------
u_id goods num
-----------------------------------------
1苹果2
2梨子 5
1西瓜 4
3葡萄 1
3 香蕉1
1橘子3
-----------------------------------------
想要的结果为:
u_id goods_sum
-----------------------------------------
1 苹果(2斤),西瓜(4斤),橘子(3斤)
2 梨子(5斤)
3 葡萄(1斤),香蕉(1斤)
---------------------------------
使用oracle的wm_concat(column)函数实现:
selectu_id,wmsys.wm_concat(goods||'('||num||'斤)')goods_sum
fromshoppinggroupbyu_id ;
---------------------------------
注意:
在不同的oracle版本中,wmsys.wm_concat 返回的数据类型不一致,10G版本中,返回的是字符串类型,11G版本中,返回的是clob类型。
如果返回的是字符串类型,则返回是有长度限制的,这时当不满足需求时,需重写该函数,返回clob字段:首先创建一个Type,一个Type Body,然后利用该Type和Type Body 创建一个返回类型为Clob的function,返回的结果是中间用逗号隔开的clob字段。
具体参见:/lowerCaseK/p/wm_concat_limit.html
WMSYS.WM_CONCAT 函數的用法
select t.rank, t.Name from t_menu_item t;
--------------------------------
我们通过 10g 所提供的 WMSYS.WM_CONCAT 函数即可以完成 行转列的效果
DEPTNO ENAME
------ ----------
例子如下:
SQL> create table idtable (id number,name varchar2(30));
Table created
SQL> insert into idtable values(10,'ab');
1 row inserted
SQL> insert into idtable values(10,'bc');
1 row inserted
SQL> insert into idtable values(10,'cd');
1 row inserted
SQL> insert into idtable values(20,'hi');
1 row inserted
SQL> insert into idtable values(20,'ij');
1 row inserted
SQL> insert into idtable values(20,'mn');
1 row inserted
SQL> select * from idtable;
---------- ------------------------------
6 rows selected
SQL> select id,wmsys.wm_concat(name) name from idtable
2 group by id;
---------- --------------------------------------------------------------------------------
SQL> select id,wmsys.wm_concat(name) over (order by id) name from idtable;
---------- --------------------------------------------------------------------------------
6 rows selected
SQL> select id,wmsys.wm_concat(name) over (order by id,name) name from idtable;
---------- --------------------------------------------------------------------------------
6 rows selected
个人觉得这个用法比较有趣.
SQL> select id,wmsys.wm_concat(name) over (partition by id) name from idtable;
---------- --------------------------------------------------------------------------------
6 rows selected
SQL> select id,wmsys.wm_concat(name) over (partition by id,name) name from idtable;
---------- --------------------------------------------------------------------------------
6 rows selected
ps:
wmsys.wm_concat、sys_connect_by_path、自定义行数实现行列转换:
CREATE TABLE tab_name(ID INTEGER NOT NULL PRIMARY KEY,cName VARCHAR2(20));
CREATE TABLE tab_name2(ID INTEGER NOT NULL,pName VARCHAR2(20));
INSERT INTO tab_name(ID,cName) VALUES (1,'百度');
INSERT INTO tab_name(ID,cName) VALUES (2,'Google');
INSERT INTO tab_name(ID,cName) VALUES (3,'网易');
INSERT INTO tab_name2(ID,pName) VALUES (1,'研发部');
INSERT INTO tab_name2(ID,pName) VALUES (1,'市场部');
INSERT INTO tab_name2(ID,pName) VALUES (2,'研发部');
INSERT INTO tab_name2(ID,pName) VALUES (2,'平台架构');
INSERT INTO tab_name2(ID,pName) VALUES (3,'研发部');
COMMIT;
期望结果:
ID
1
2
3
方法一:使用wmsys.wm_concat()
SELECT t1.ID,ame,wmsys.wm_concat(t2.pName) FROM tab_name t1,tab_name2 t2 WHERE t1.ID=t2.ID GROUP BY ame,t1.id;
方法二:使用sys_connect_by_path
select id, cName, ltrim(max(sys_connect_by_path(pName, ',')), ',') from (select row_number() over(PARTITION by t1.id ORDER by cName) r,t1.*, t2.pName from tab_name t1, tab_name2 t2 where t1.id = t2.id)
start with r=1 CONNECT by prior r =r-1 and prior id = id group by id ,cName order by id;
方法三:使用自定义函数
create or replace function coltorow(midId INT) RETURN VARCHAR2 is
Result VARCHAR2(1000);
begin
FOR cur IN (SELECT pName FROM tab_name2 t2 WHERE midId=t2.id) LOOP
RESULT:=RESULT||cur.pName||',';
END LOOP;
RESULT:=rtrim(RESULT,',');
return(Result);
end coltorow;
SELECT t1.*,coltorow(t1.ID) FROM tab_name t1,tab_name2 t2 WHERE t1.ID=t2.ID GROUP BY t1.ID,ame ORDER BY t1.ID;