詳解Mysql 游標(biāo)的用法及其作用

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BEGIN 
 
--定義變量 
declare testrangeid BIGINT; 
declare versionid BIGINT; 
declare done int; 
--創(chuàng)建游標(biāo)，并存儲(chǔ)數(shù)據(jù) 
declare cur_test CURSOR for 
 select id as testrangeid,version_id as versionid from tp_testrange; 
--游標(biāo)中的內(nèi)容執(zhí)行完后將done設(shè)置為1 
 DECLARE CONTINUE HANDLER FOR NOT FOUND SET done=1; 
--打開(kāi)游標(biāo) 
open cur_test; 
--執(zhí)行循環(huán) 
 posLoop:LOOP 
--判斷是否結(jié)束循環(huán) 
  IF done=1 THEN 
  LEAVE posLoop; 
 END IF; 
--取游標(biāo)中的值 
 FETCH cur_test into testrangeid,versionid; 
--執(zhí)行更新操作 
 update tp_data_execute set version_id=versionid where testrange_id = testrangeid; 
 END LOOP posLoop; 
--釋放游標(biāo) 
CLOSE cur_test; 
 
END 
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--在windows系統(tǒng)中寫(xiě)存儲(chǔ)過(guò)程時(shí)，如果需要使用declare聲明變量，需要添加這個(gè)關(guān)鍵字，否則會(huì)報(bào)錯(cuò)。 
delimiter // 
drop procedure if exists StatisticStore; 
CREATE PROCEDURE StatisticStore() 
BEGIN 
 --創(chuàng)建接收游標(biāo)數(shù)據(jù)的變量 
 declare c int; 
 declare n varchar(20); 
 --創(chuàng)建總數(shù)變量 
 declare total int default 0; 
 --創(chuàng)建結(jié)束標(biāo)志變量 
 declare done int default false; 
 --創(chuàng)建游標(biāo) 
 declare cur cursor for select name,count from store where name = 'iphone'; 
 --指定游標(biāo)循環(huán)結(jié)束時(shí)的返回值 
 declare continue HANDLER for not found set done = true; 
 --設(shè)置初始值 
 set total = 0; 
 --打開(kāi)游標(biāo) 
 open cur; 
 --開(kāi)始循環(huán)游標(biāo)里的數(shù)據(jù) 
 read_loop:loop 
 --根據(jù)游標(biāo)當(dāng)前指向的一條數(shù)據(jù) 
 fetch cur into n,c; 
 --判斷游標(biāo)的循環(huán)是否結(jié)束 
 if done then 
  leave read_loop; --跳出游標(biāo)循環(huán) 
 end if; 
 --獲取一條數(shù)據(jù)時(shí)，將count值進(jìn)行累加操作，這里可以做任意你想做的操作， 
 set total = total + c; 
 --結(jié)束游標(biāo)循環(huán) 
 end loop; 
 --關(guān)閉游標(biāo) 
 close cur; 
 
 --輸出結(jié)果 
 select total; 
END; 
--調(diào)用存儲(chǔ)過(guò)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;

--判斷游標(biāo)的循環(huán)是否結(jié)束 
if done then 
 leave read_loop; --跳出游標(biāo)循環(huán) 
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; 
--如果有多個(gè)參數(shù)用逗號(hào)分隔 
execute s1 using @condition1; 
--手工釋放，或者是 connection 關(guān)閉時(shí)， server 自動(dòng)回收 
deallocate prepare s1;