MySQL 游标的定义与使用方式

CREATE TABLE IF NOT EXISTS `store` (
 `id` int(11) NOT NULL AUTO_INCREMENT,
 `name` varchar(20) NOT NULL,
 `count` int(11) NOT NULL DEFAULT '1',
 PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=7;
 
INSERT INTO `store` (`id`, `name`, `count`) VALUES
(1, 'android', 15),
(2, 'iphone', 14),
(3, 'iphone', 20),
(4, 'android', 5),
(5, 'android', 13),
(6, 'iphone', 13);

--在windows系统中写存储过程时，如果需要使用declare声明变量，需要添加这个关键字，否则会报错。
delimiter //
drop procedure if exists StatisticStore;
CREATE PROCEDURE StatisticStore()
BEGIN
  --创建接收游标数据的变量
  declare c int;
  declare n varchar(20);
  --创建总数变量
  declare total int default 0;
  --创建结束标志变量
  declare done int default false;
  --创建游标
  declare cur cursor for select name,count from store where name = 'iphone';
  --指定游标循环结束时的返回值
  declare continue HANDLER for not found set done = true;
  --设置初始值
  set total = 0;
  --打开游标
  open cur;
  --开始循环游标里的数据
  read_loop:loop
  --根据游标当前指向的一条数据
  fetch cur into n,c;
  --判断游标的循环是否结束
  if done then
    leave read_loop;  --跳出游标循环
  end if;
  --获取一条数据时，将count值进行累加操作，这里可以做任意你想做的操作，
  set total = total + c;
  --结束游标循环
  end loop;
  --关闭游标
  close cur;
 
  --输出结果
  select total;
END;
--调用存储过程
call StatisticStore();

read_loop:loop
fetch cur into n,c;
set total = total+c;
end loop;

declare continue HANDLER for not found set done = true;

--判断游标的循环是否结束
if done then
  leave read_loop;  --跳出游标循环
end if;

drop procedure if exists StatisticStore1;
CREATE PROCEDURE StatisticStore1()
BEGIN
  declare c int;
  declare n varchar(20);
  declare total int default 0;
  declare done int default false;
  declare cur cursor for select name,count from store where name = 'iphone';
  declare continue HANDLER for not found set done = true;
  set total = 0;
  open cur;
  fetch cur into n,c;
  while(not done) do
    set total = total + c;
    fetch cur into n,c;
  end while;
  
  close cur;
  select total;
END;
 
call StatisticStore1();

drop procedure if exists StatisticStore2;
CREATE PROCEDURE StatisticStore2()
BEGIN
  declare c int;
  declare n varchar(20);
  declare total int default 0;
  declare done int default false;
  declare cur cursor for select name,count from store where name = 'iphone';
  declare continue HANDLER for not found set done = true;
  set total = 0;
  open cur;
  repeat
  fetch cur into n,c;
  if not done then
    set total = total + c;
  end if;
  until done end repeat;
  close cur;
  select total;
END;
 
call StatisticStore2();

drop procedure if exists StatisticStore3;
CREATE PROCEDURE StatisticStore3()
BEGIN
  declare _n varchar(20);
  declare done int default false;
  declare cur cursor for select name from store group by name;
  declare continue HANDLER for not found set done = true;
  open cur;
  read_loop:loop
  fetch cur into _n;
  if done then
    leave read_loop;
  end if;
  begin
    declare c int;
    declare n varchar(20);
    declare total int default 0;
    declare done int default false;
    declare cur cursor for select name,count from store where name = 'iphone';
    declare continue HANDLER for not found set done = true;
    set total = 0;
    open cur;
    iphone_loop:loop
    fetch cur into n,c;
    if done then
      leave iphone_loop;
    end if;
    set total = total + c;
    end loop;
    close cur;
    select _n,n,total;
  end;
  begin
      declare c int;
      declare n varchar(20);
      declare total int default 0;
      declare done int default false;
      declare cur cursor for select name,count from store where name = 'android';
      declare continue HANDLER for not found set done = true;
      set total = 0;
      open cur;
      android_loop:loop
      fetch cur into n,c;
      if done then
        leave android_loop;
      end if;
      set total = total + c;
      end loop;
      close cur;
    select _n,n,total;
  end;
  begin
  
  end;
  end loop;
  close cur;
END;
 
call StatisticStore3();

set @sqlStr='select * from table where condition1 = ?';
prepare s1 for @sqlStr;
--如果有多个参数用逗号分隔
execute s1 using @condition1;
--手工释放，或者是 connection 关闭时， server 自动回收
deallocate prepare s1;