oracle使用聚合函数实现 多行合并
COUNTRY              CITY
-------------------- --------------------
中国                 台北
中国                 香港
中国                 上海
日本                 东京
日本                 大阪

COUNTRY              CITY
-------------------- --------------------
中国                 台北  香港  上海
日本                 东京   大阪

select country,strcat(city) from t_city group by country

1.创建类型

create or replace type strcat_type as object (
cat_string varchar2(4000),
static function ODCIAggregateInitialize(cs_ctx In Out strcat_type) return number,
member function ODCIAggregateIterate(self In Out strcat_type,value in varchar2) return
number,
member function ODCIAggregateMerge(self In Out strcat_type,ctx2 In Out strcat_type)
return number,
member function ODCIAggregateTerminate(self In Out strcat_type,returnValue Out
varchar2,flags in number) return number
);



2. 创建类型体

create or replace type body strcat_type is
  static function ODCIAggregateInitialize(cs_ctx IN OUT strcat_type) return number
  is
  begin
      cs_ctx := strcat_type( null );
      return ODCIConst.Success;
  end;

  member function ODCIAggregateIterate(self IN OUT strcat_type,
                                       value IN varchar2 )
  return number
  is
  begin
      self.cat_string := self.cat_string || ';'|| value;
      return ODCIConst.Success;
  end;

  member function ODCIAggregateTerminate(self IN Out strcat_type,
                                         returnValue OUT varchar2,
                                         flags IN number)
  return number
  is
  begin
      returnValue := ltrim(rtrim(self.cat_string,';'),';');
      return ODCIConst.Success;
  end;

  member function ODCIAggregateMerge(self IN OUT strcat_type,
                                     ctx2 IN Out strcat_type)
  return number
  is
  begin
      self.cat_string := self.cat_string || ';' || ctx2.cat_string;
      retu