详解Mysql 游标的用法及其作用

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BEGIN 
 
--定义变量 
declare testrangeid BIGINT; 
declare versionid BIGINT; 
declare done int; 
--创建游标，并存储数据 
declare cur_test CURSOR for 
 select id as testrangeid,version_id as versionid from tp_testrange; 
--游标中的内容执行完后将done设置为1 
 DECLARE CONTINUE HANDLER FOR NOT FOUND SET done=1; 
--打开游标 
open cur_test; 
--执行循环 
 posLoop:LOOP 
--判断是否结束循环 
  IF done=1 THEN 
  LEAVE posLoop; 
 END IF; 
--取游标中的值 
 FETCH cur_test into testrangeid,versionid; 
--执行更新操作 
 update tp_data_execute set version_id=versionid where testrange_id = testrangeid; 
 END LOOP posLoop; 
--释放游标 
CLOSE cur_test; 
 
END 
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--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;