用Oracle自定义聚合函数实现字符串连接的聚合

create or replace type string_sum_obj as object (

--聚合函数的实质就是一个对象

    sum_string varchar2(4000),

    static function ODCIAggregateInitialize(v_self in out string_sum_obj) return number,
    --对象初始化

    member function ODCIAggregateIterate(self in out string_sum_obj, value in varchar2) return number,
    --聚合函数的迭代方法(这是最重要的方法)

    member function ODCIAggregateMerge(self in out string_sum_obj, v_next in string_sum_obj) return number,
    --当查询语句并行运行时,才会使用该方法,可将多个并行运行的查询结果聚合
   
    member function ODCIAggregateTerminate(self in string_sum_obj, return_value out varchar2 ,v_flags in number) return number
    --终止聚集函数的处理,返回聚集函数处理的结果.
)
/
create or replace type body string_sum_obj is

    static function ODCIAggregateInitialize(v_self in out string_sum_obj) return number is
    begin
        v_self := string_sum_obj(null);
        return ODCICONST.Success;
    end;

    member function ODCIAggregateIterate(self in out string_sum_obj, value in varchar2) return number is
    begin
         /* 连接 */ 
         self.sum_string := self.sum_string || value;
         return ODCICONST.Success;
         /* 最大值 */
         if self.sum_string<value then
             self.sum_string:=value;
         end if;
         /* 最小值 */
         if self.sum_string>value then
             self.sum_string:=value;        
         end if;
        
         return ODCICONST.Success;
    end;

    member function ODCIAggregateMerge(self in out string_sum_obj, v_next in string_sum_obj) return number is
    begin
         /* 连接 */ 
         self.sum_string := self.sum_string || v_next.sum_string;
         return ODCICONST.Success;
         /* 最大值 */
         if self.sum_string<v_next.sum_string then
             self.sum_string:=v_next.sum_string;
         end if;
         /* 最小值 */
         if self.sum_string>v_next.sum_string then
             self.sum_string:=v_next.sum_string;        
         end if;
        
         return ODCICONST.Success;
    end;

    member function ODCIAggregateTerminate(self in string_sum_obj, return_value out varchar2 ,v_flags in number) return number is
    begin
         return_value:= self.sum_string;
         return ODCICONST.Success;
    end;

end;
/
create or replace function ConnStrSum(value Varchar2) return Varchar2
    parallel_enable aggregate using string_sum_obj;