SQL> select * from test;

ID MC
---------- -------------
1 11111
1 22222
2 11111
2 22222
3 11111
3 22222
3 33333

已选择7行。

SQL> select id,ltrim(max(sys_connect_by_path(mc,',')),',') row2col
from (select id,mc,
id+(row_number() over(order by id)) node_id,
row_number() over(partition by id order by id) rn
from test)
start with rn = 1
connect by node_id-1 = prior node_id
group by id
order by id;

ID ROW2COL
---------- -------------------------------------------------------------
1 11111,22222
2 11111,22222
3 11111,22222,33333

SQL> select id,replace(max(sys_connect_by_path(mc,',')),',') row2col
from (select id,mc,
id+(row_number() over(order by id)) node_id,
row_number() over(partition by id order by id) rn
from test)
start with rn = 1
connect by node_id-1 = prior node_id
group by id
order by id;

ID ROW2COL
---------- ------------------------------------------------------------
1 1111122222
2 1111122222
3 111112222233333

--该测试脚本可以直接运行

--现在想把数据库中数据按照固定字段分组相加，这里总结了三种方法。

--创建测试表、添加测试数据

create table test(id varchar2(10),mc varchar2(50));
insert into test values('1','11111');
insert into test values('1','22222');
insert into test values('2','11111');
insert into test values('2','22222');
insert into test values('3','11111');
insert into test values('3','22222');
insert into test values('3','33333');
commit;

--方法一：

set serveroutput on size 1000000
declare
union_mc varchar2(200);
begin
for cur_a in(select distinct id from test) loop
for cur_b in(select mc from test where id=cur_a.id) loop
union_mc:=union_mc||cur_b.mc;
end loop;
dbms_output.put_line(cur_a.id||chr(9)||union_mc);
union_mc := '';
end loop;
end;
/

--方法二：

CREATE OR REPLACE function link(v_id varchar2)
return varchar2
is
union_mc varchar2(200);
begin
for cur in (select mc from test where id=v_id) loop
union_mc := union_mc||cur.mc;
end loop;
union_mc := rtrim(union_mc,1);
return union_mc;
end;
/

select id,link(id) from test group by id;

--方法三：

/*从Oracle 9i开始，开发者可以创建用户自定义的合计函数，除了PL/SQL外，还可以使用任何Oralce所支持的语言（如C＋＋或者Java）来创建合计函数。TYPE头定义必须包含ODCIAggregateInitialize、ODCIAggregateIterate、ODCIAggregateMerge和ODCIAggregateTerminate这四个接口函数。*/

/*Initialize函数对数据组各个需要处理的字段各运行一次。自然的，我需要为每一个值准备一个新的清单，所以需要初始化持久变量list，这里初始化值为null。*/

/*Iterate函数处理返回的行，所以实际上是由它来创建返回的值的清单。先测试list是否为空，如果为空，就把list直接设置为所引入的value值；如果list变量非空，则给list添加一个逗号后再插入value值，list的最大允许字符数32767。*/

/*Terminate函数在数据组的每个行的感兴趣字段数据被处理后执行。在这个函数中我只需简单的返回清单变量即可。*/

/*Merge函数，用来返回成功标记的。*/

/*创建自己的合计函数扩展了Oracle统计和文本处理能力。*/

create or replace type t_cat as object
(
union_mc VARCHAR2(200),
static function ODCIAggregateInitialize(sctx IN OUT t_cat) return number,
member function ODCIAggregateIterate(self IN OUT t_cat,value IN varchar2) return number,
member function ODCIAggregateTerminate(self IN t_cat,returnValue OUT varchar2, flags IN number) return number,
member function ODCIAggregateMerge(self IN OUT t_cat,ctx2 IN t_cat) return number
);

create or replace type body t_cat is
static function ODCIAggregateInitialize(sctx IN OUT t_cat )
return number is
begin
sctx := t_cat('');
return ODCIConst.Success;
end;

member function ODCIAggregateIterate(self IN OUT t_cat, value IN varchar2)
return number is
begin
self.union_mc := self.union_mc || value;
return ODCIConst.Success;
end;

member function ODCIAggregateTerminate(self IN t_cat, returnValue OUT varchar2, flags IN number) return number is
begin
returnValue := self.union_mc;
return ODCIConst.Success;
end;

member function ODCIAggregateMerge(self IN OUT t_cat , ctx2 IN t_cat ) return number is
begin
return ODCIConst.Success;
end;
end;
/

/*如果你的Oracle服务器没有配置成支持并行处理的方式，可以去掉参数PARALLEL_ENABLE*/

create or replace function catstr(v_mc varchar2) return varchar2 PARALLEL_ENABLE AGGREGATE USING t_cat;
/

select id,catstr(mc) from test group by id;