oracle wmsys.wm_concat用法

作用：oracle内置函数wmsys.wm_concat用来以逗号分隔连接列的值

1）测试sql语句如下： 

 SELECT id, wmsys.wm_concat(val) val
   FROM (SELECT 1 id, 'a' val
          FROM dual
        UNION ALL
        SELECT 2 id, 't' val
          FROM dual
        UNION ALL
        SELECT 1 id, 'd' val
          FROM dual
        UNION ALL
        SELECT 2 id, 'e' val FROM dual)
 GROUP BY id

     查询输出：