oracle 分组拼接

　　方法一：listagg， 参考链接，从oracle11g后出现的新函数

　　如果拼接的字符串长度超过4000字节，会报ora-01489错误，ora-01489 字符串连接的结果过长 解决方案。

SELECT
	id,count(name) as countname,
	LISTAGG(to_char(name), ',') WITHIN GROUP(ORDER BY name) AS pjname
FROM
(
	select
		distinct B.id as id,
		B.name as name
	from
		B left join C on B.name = C.name
	where
		C.gender = 'female'
)
group by id

　　方法二：wmsys.wm_concat，参考链接，返回结果类型会受版本影响，不建议使用

select
	grp, wmsys.wm_concat(str)
from
(
	select 1 grp, 'a1' str from dual
    union
    select 1 grp, 'a2' str from dual
    union
    select 2 grp, 'b1' str from dual
    union
    select 2 grp, 'b2' str from dual
    union
    select 2 grp, 'b3' str from dual
) t
group by
	grp

　　方法三（1）：sys_connect_by_path，参考链接

select role_category,
       ltrim(sys_connect_by_path(role_id, ','), ',') as role_id_list
from   (
        select role_category,
               role_id,
               (row_number() over(partition by role_category order by role_id))
                  as row_number
        from   (
                select 'role_01' as role_id ,'admin' as role_category from dual
                union all
                select 'role_02' as role_id ,'admin' as role_category from dual
                union all
                select 'role_03' as role_id ,'normal' as role_category from dual
                union all
                select 'role_04' as role_id ,'normal' as role_category from dual
                union all
                select 'role_05' as role_id ,'normal' as role_category from dual
                union all
                select 'role_06' as role_id ,'normal' as role_category from dual
                union all
                select 'role_07' as role_id ,'normal' as role_category from dual
                union all
                select 'role_08' as role_id ,'normal' as role_category from dual
               )
       )
where  connect_by_isleaf = 1
       start with row_number = 1
       connect by row_number - 1 = prior row_number
       and role_category = prior role_category

　　方法三（2）：sys_connect_by_path，参考链接

select
	deptno,
	ltrim(max(sys_connect_by_path(ename, ',')), ',') name
from
(
	select
		deptno,
		ename,
		row_number() over(partition by deptno order by ename) ro
    from
	(
		select
			deptno,ename
		from
			emp
		where
			deptno is not null
	) t
) newtab
start with newtab.ro = 1
connect by prior newtab.ro = newtab.ro - 1
group by deptno;

　　方法三（3）：sys_connect_by_path，参考链接

select
	deptno,
	ltrim(max(sys_connect_by_path(ename, ',')), ',') name
from
(
	select
		deptno,
		ename,
		ro,
		lead(ro) over(partition by deptno order by ro) ro_next
    from
	(
		select
			deptno, ename,
			row_number() over(order by deptno, ename) ro
		from
			emp
		where
			deptno is not null
	) t
) newtab
start with ro_next is null
connect by ro_next = prior ro
group by deptno;