oracle

 

NOTE:特别声明一下内容转自网络
http://www.ningoo.net/html/2008/how_to_do_string_aggregate_on_oracle.html

假如有如下表，其中各个i值对应的行数是不定的

 

SQL> select * from t;

         I A          D
---------- ---------- -------------------
         1 b          2008-03-27 10:55:42
         1 a          2008-03-27 10:55:46
         1 d          2008-03-27 10:55:30
         2 z          2008-03-27 10:55:55
         2 t          2008-03-27 10:55:59

--- 要获得如下结果，注意字符串需要按照D列的时间排序：

1  d,b,a
2  z,t

 

方法一：使用自定义函数

确定：遇到数据量大时，性能会非常差

 

create or replace function my_concat(n number)
return varchar2
is
 type typ_cursor is ref cursor;
 v_cursor typ_cursor;
 v_temp varchar2(10);
 v_result varchar2(4000):= '';
 v_sql varchar2(200);
begin
 v_sql := 'select a from t where i=' || n ||' order by d';
 open v_cursor for v_sql;
 loop
    fetch v_cursor into v_temp;
    exit when v_cursor%notfound;
    v_result := v_result ||',' || v_temp;
 end loop;
 return substr(v_result,2);
end;

SQL> select i,my_concat(i) from t group by i;

         I MY_CONCAT(I)
---------- --------------------
         1 d,b,a
         2 z,t

 

方法二：使用sys_connect_by_path

select i,ltrim(max(sys_connect_by_path(a,',')),',') a
from
(
select i,a,d,min(d) over(partition by i) d_min,
(row_number() over(order by i,d))+(dense_rank() over (order by i)) numid
from t
)
start with d=d_min connect by numid-1=prior numid
group by i;

 

方法三：使用wm_sys.wm_concat

SQL> select i,wmsys.wm_concat(a) from t group by i;

         I WMSYS.WM_CONCAT(A)
---------- --------------------
         1 b,a,d
         2 z,t

SQL> select i,wmsys.wm_concat(a)
  2  from
  3  (select * from t order by i,d)
  4  group by i;

         I WMSYS.WM_CONCAT(A)
---------- --------------------
         1 d,b,a
         2 z,t