-- 一个奇怪的My SQL游标循环问题 --

-- 我的一个函数

-- 其作用是生成一个可执行的SQL语句，

-- 目的是生成“查询一张表的int类型字段的所有max、min、avg值”的SQL语句的函数：



DELIMITER $$



CREATE FUNCTION get_tb_numberInfo(v_tb_name varchar(50))

  RETURNS VARCHAR(2000) CHARSET utf8

BEGIN

  DECLARE v_sql varchar(20000);



  DECLARE v_column_name varchar(200);

  DECLARE v_column_name_min varchar(200);

  DECLARE v_column_name_max varchar(200);

  DECLARE v_column_name_avg varchar(200);

  DECLARE no_more_departments boolean;



  DECLARE get_tbInfo CURSOR FOR

    SELECT column_name FROM information_schema.columns 

     WHERE UPPER(TABLE_NAME)=upper(v_tb_name)

       AND TABLE_SCHEMA=(select database())

       AND DATA_TYPE IN('bigint','int','decimal');



  DECLARE CONTINUE HANDLER FOR NOT FOUND SET no_more_departments=1;

  SET no_more_departments=0; 

  SET v_sql := 'SELECT ';

  OPEN get_tbInfo;

  REPEAT

  -- Get get_tbInfo 

  FETCH get_tbInfo INTO v_column_name;

    SET v_column_name_min = concat('min(',v_column_name,') as ',v_column_name,'_min,');

    SET v_column_name_max = concat('max(',v_column_name,') as ',v_column_name,'_max,');

    SET v_column_name_avg = concat('avg(',v_column_name,') as ',v_column_name,'_avg,');

    SET v_sql = concat(v_sql,v_column_name_min,v_column_name_max,v_column_name_avg,'\n');

  UNTIL no_more_departments

  END REPEAT;

  CLOSE get_tbInfo;



  SET v_sql = substring(v_sql,1,length(v_sql)-1);

  SET v_sql = concat(v_sql,' from ',v_tb_name,';');



  RETURN v_sql;

END;

$$



delimiter ;



-- 但是：我每次执行后，最后一个字段生成了两次：min、max、avg字段，例如：

mysql> select get_tb_numberInfo('f_union_refer_date_index');



 SELECT

min(date_id) as date_id_min,max(date_id) as date_id_max,avg(date_id) as date_id_avg,

min(refer_id) as refer_id_min,max(refer_id) as refer_id_max,avg(refer_id) as refer_id_avg,

min(ip_num) as ip_num_min,max(ip_num) as ip_num_max,avg(ip_num) as ip_num_avg,

min(direct_pv_num) as direct_pv_num_min,max(direct_pv_num) as direct_pv_num_max,avg(direct_pv_num) as direct_pv_num_avg,

min(indirect_pv_num) as indirect_pv_num_min,max(indirect_pv_num) as indirect_pv_num_max,avg(indirect_pv_num) as indirect_pv_num_avg,

min(direct_cv_num) as direct_cv_num_min,max(direct_cv_num) as direct_cv_num_max,avg(direct_cv_num) as direct_cv_num_avg,

min(indirect_cv_num) as indirect_cv_num_min,max(indirect_cv_num) as indirect_cv_num_max,avg(indirect_cv_num) as indirect_cv_num_avg,

min(direct_uv_num) as direct_uv_num_min,max(direct_uv_num) as direct_uv_num_max,avg(direct_uv_num) as direct_uv_num_avg,

min(new_uv_num) as new_uv_num_min,max(new_uv_num) as new_uv_num_max,avg(new_uv_num) as new_uv_num_avg,

min(new_uv_num) as new_uv_num_min,max(new_uv_num) as new_uv_num_max,avg(new_uv_num) as new_uv_num_avg from f_union_refer_date_index;



-- 请问是怎么回事儿呢？有什么办法解决不？