如何将结果输出为一行

oracle将返回结果放在一行
有时我们需要将返回结果放到一行中，比如
select * from 
(select username from dba_users
order by username)
where rownum<10;

USERNAME
------------------------------
ANONYMOUS
APEX_030200
APEX_PUBLIC_USER
APPQOSSYS
CTXSYS
DBSNMP
DIP
EXFSYS
FLOWS_FILES

9 rows selected.

想把上的结果变为一行，并用逗号分隔
ANONYMOUS,APEX_030200,APEX_PUBLIC_USER,APPQOSSYS,CTXSYS,DBSNMP,DIP,EXFSYS,FLOWS_FILES

办法：使用wmsys.wm_concat() 可以实现。
注意！wmsys.wm_concat()自动会在每列后面加上逗号。

set linesize 120
select wmsys.wm_concat(t.username)  from 
(select username  from dba_users
order by username) t
where rownum<10;

WMSYS.WM_CONCAT(T.USERNAME)
------------------------------------------------------------------------------------------------------------------------
ANONYMOUS,APEX_030200,APEX_PUBLIC_USER,APPQOSSYS,CTXSYS,DBSNMP,DIP,EXFSYS,FLOWS_FILES


如果涉及到多列，只需要将列放在该函数中，并已逗号分隔即可
set linesize 120
select wmsys.wm_concat(t.USER_ID||':'||t.username)  from 
(select username,USER_ID  from dba_users
order by username) t
where rownum<10;

WMSYS.WM_CONCAT(T.USER_ID||':'||T.USERNAME)
------------------------------------------------------------------------------------------------------------------------
46:ANONYMOUS,78:APEX_030200,76:APEX_PUBLIC_USER,31:APPQOSSYS,43:CTXSYS,30:DBSNMP,14:DIP,42:EXFSYS,75:FLOWS_FILES