文章转载http://www.2cto.com/database/201204/128928.html
首先介绍语法：
wmsys.wm_concat
Definition:
The
Oracle PL/SQL WM_CONCAT function is used to aggregate data from a number of rows into a single row, giving a list of data associated with a specific value. In effect, it cross-tabulates a comma delimited list.
Note that
WM_CONCAT is undocumented and unsupported by Oracle, meaning it should not be used in production systems.
The LISTAGG function, which can produce the same output asWM_CONCAT is both documented and supported by Oracle.
例子：
[sql]
select t1.main_id,
to_char(wmsys.wm_concat(t1.send_id || '||' || t2.realname || '||' ||
t2.IMG_PATH)) sendidlist
from LCMS_SEND_USER t1, LCMS_USER_STUD t2
group by t1.main_id;
结果：
网络中也有这样使用：
下面只是收藏：
[sql]
SQL> select id,wmsys.wm_concat(name) over (order by id) name from idtable;
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ID NAME
---------- --------------------------------------------------------------------------------
10 ab,bc,cd
10 ab,bc,cd
10 ab,bc,cd
20 ab,bc,cd,hi,ij,mn
20 ab,bc,cd,hi,ij,mn
20 ab,bc,cd,hi,ij,mn
6 rows selected
[sql]
SQL> select id,wmsys.wm_concat(name) over (order by id,name) name from idtable;
ID NAME
---------- --------------------------------------------------------------------------------
10 ab
10 ab,bc
10 ab,bc,cd
20 ab,bc,cd,hi
20 ab,bc,cd,hi,ij
20 ab,bc,cd,hi,ij,mn
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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;
ID NAME
---------- --------------------------------------------------------------------------------
10 ab,bc,cd
10 ab,bc,cd
10 ab,bc,cd
20 hi,ij,mn
20 hi,ij,mn
20 hi,ij,mn
6 rows selected
SQL> select id,wmsys.wm_concat(name) over (partition by id,name) name from idtable;
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ID NAME
---------- --------------------------------------------------------------------------------
10 ab
10 bc
10 cd
20 hi
20 ij
20 mn
6 rows selected
作者 psyuhen