用到Oralce10g以后增加的函数wmsys.wm_concat
例如这张表的有两个字段，要按airport_id合并成两行可用sql语句
select airport_id, wmsys.wm_concat( account) from AIRPORT_MODIFY group by airport_id
结果为：
非常简单，美中不足的是合并结果没有排序，解决排序问题最简单的办法就是在合并列前加上distinct
此外，如果合并列结果出现乱码，需要在合并列前加上to_char(),如wmsys.wm_concat( to_char(account)),据说是因为该函数在不同的Oracle版本中会返回varchar2或CLob两种结果
2016.8.15补充，关于排序
按wmsys.wm_concat(distinct account)排序只能实现按account文本排序，无法实现按某复杂逻辑排序。下面是实现方法
有普通sql如下
select flt,srtnum,seg,tran_level,name
from flight_tran_direction
where seg>0
order by flt,seg,srtnum
结果为：列举所有航线中，高度层反配的所有点
要实现按flt，seg分组并按srtsum排序的各点串，可写sql为
select flt,seg,tran_level,
WMSYS.WM_CONCAT(name) OVER(PARTITION BY flt,seg ORDER BY srtnum) KEY
from flight_tran_direction
where seg>0
order by flt,seg
结果为：类似于group by flt,seg实现了按flt,seg分组,且name按srtnum逻辑排序。唯一不足的是一个分组会多出若干历史行。实际上只需要每组最后一行。
改进sql为：外面再嵌套一层groupby结构，通过max实现取最多的合并列
select flt,seg,max(key) rt
from
(
select flt,seg,tran_level,
WMSYS.WM_CONCAT(name) OVER(PARTITION BY flt,seg ORDER BY srtnum) KEY
from flight_tran_direction
where seg>0
order by flt,seg
)
group by flt,seg,tran_level
结果为：
甚至反过按合并列rt分组，组合flt
select rt,tran, WMSYS.WM_CONCAT( distinct flt)
from
(
select flt,seg,
case mod(to_number(regexp_substr(tran_level,'^[[:digit:]]+')),2) when 1 then '西单' else '东双' end tran,
replace(max(key),',','-') rt
from
(
select flt,seg,tran_level,
WMSYS.WM_CONCAT(name) OVER(PARTITION BY flt,seg ORDER BY srtnum) KEY
from flight_tran_direction
where seg>0
order by flt,seg
)
group by flt,seg,tran_level
)
group by rt,tran
order by rt,tran
