构建测试表：
create table TABLE1
(
ID INTEGER,
NAME VARCHAR2(10)
)
create table TABLE2
(
ID INTEGER,
ROLE VARCHAR2(10)
)
insert into TABLE1 (ID, NAME) values (1, '张三');
insert into TABLE1 (ID, NAME) values (2, '李四');
commit;
insert into TABLE2 (ID, ROLE) values (1, '查询');
insert into TABLE2 (ID, ROLE) values (1, '分析');
insert into TABLE2 (ID, ROLE) values (1, '决策');
insert into TABLE2 (ID, ROLE) values (2, '查询');
commit;
要求输出结果：
ID NAME ROLE
1 张三查询,分析,决策
2 李四查询
方法一、使用wmsys.wm_concat
select table1.*,wmsys.wm_concat(role) from table1,table2 where table1.id=table2.id
group by table1.id,table1.name
方法二、使用sys_connect_by_path
select id, name, ltrim(max(sys_connect_by_path(role, ',')), ',') from
(select row_number() over(partition by table1.id order by name) rn,table1.*, role from table1, table2 where table1.id = table2.id)
start with rn = 1
connect by prior rn = rn - 1 and prior id = id
group by id, name
order by id
方法三、使用自定义函数
create or replace function my_concat(mid in integer) return varchar2
--记住：参数和返回值里的数据类型都不用定义长度
is
result varchar2(4000); --定义变量，记住Oracle中定义变量不需要
begin
for temp_cursor in (select role from table2 where id=mid) loop
--此处在游标FOR循环中使用查询
result :=result || temp_cursor.role || ',';
--Oracle中字符连接使用||，而sql server中用+
end loop;
result := rtrim(result,',');
--去掉最后一个空格,还有Oracle中的赋值前面没有set
return result;
end;
select table1.*,my_concat(table1.id) from table1,table2 where table1.id=table2.id
group by table1.id,table1.name
order by table1.id