創(chuàng)建游標(biāo)
首先在MySql中創(chuàng)建一張數(shù)據(jù)表：
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);
我們現(xiàn)在要用存儲(chǔ)過(guò)程做一個(gè)功能碘耳，統(tǒng)計(jì)iphone的總庫(kù)存是多少，并把總數(shù)輸出到控制臺(tái)框弛。
--在windows系統(tǒng)中寫(xiě)存儲(chǔ)過(guò)程時(shí)辛辨，如果需要使用declare聲明變量，需要添加這個(gè)關(guān)鍵字瑟枫，否則會(huì)報(bào)錯(cuò)斗搞。
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)行累加操作慷妙，這里可以做任意你想做的操作僻焚，
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();
fetch是獲取游標(biāo)當(dāng)前指向的數(shù)據(jù)行，并將指針指向下一行膝擂，當(dāng)游標(biāo)已經(jīng)指向最后一行時(shí)繼續(xù)執(zhí)行會(huì)造成游標(biāo)溢出虑啤。
使用loop循環(huán)游標(biāo)時(shí)，他本身是不會(huì)監(jiān)控是否到最后一條數(shù)據(jù)了架馋，像下面代碼這種寫(xiě)法狞山，就會(huì)造成死循環(huán)；
read_loop:loop
fetch cur into n,c;
set total = total+c;
end loop;
在MySql中叉寂，造成游標(biāo)溢出時(shí)會(huì)引發(fā)mysql預(yù)定義的NOT FOUND錯(cuò)誤萍启，所以在上面使用下面的代碼指定了當(dāng)引發(fā)not found錯(cuò)誤時(shí)定義一個(gè)continue 的事件，指定這個(gè)事件發(fā)生時(shí)修改done變量的值屏鳍。
declare continue HANDLER for not found set done = true;
所以在循環(huán)時(shí)加上了下面這句代碼：
--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;
如果done的值是true勘纯，就結(jié)束循環(huán)。繼續(xù)執(zhí)行下面的代碼钓瞭。
使用方式
游標(biāo)有三種使用方式：第一種就是上面的實(shí)現(xiàn)驳遵，使用loop循環(huán)；第二種方式如下降淮，使用while循環(huán)：
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;
第三種方式是使用repeat執(zhí)行：
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;
游標(biāo)嵌套
在mysql中超埋，每個(gè)begin end 塊都是一個(gè)獨(dú)立的scope區(qū)域，由于MySql中同一個(gè)error的事件只能定義一次佳鳖，如果多定義的話(huà)在編譯時(shí)會(huì)提示Duplicate handler declared in the same block霍殴。
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();
轉(zhuǎn)載：http://blog.csdn.net/liguo9860/article/details/50848216
