mysql基本游标

2024-07-24 12:32:05

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mysql基础游标：

一、游标的定义：

create procedure p12()
begin

declare row_name varchar(20);
declare row_num int;

declare myCursor cursor for select name,num from goods;//定义游标myCursor

open myCursor;//打开游标myCursor

fetch myCursor into row_name,row_num;//使用游标myCursor获取第一行

select row_name, row_num;

fetch myCursor into row_name,row_num;//使用游标myCursor获取第二行；每fetch一次游标就自动往下游一次.

select row_name, row_num;

close myCursor;//关闭游标myCursor

end;

二、游标+repeat循环-->实现遍历行：
create procedure p13()
begin

declare row_gid int;
declare row_name varchar(20);
declare row_num int;

declare row_count int;
declare i int default 0;

declare myCursor cursor for select gid,name,num from goods;

select count(1) into row_count from goods;

open myCursor;

repeat

fetch myCursor into row_gid,row_name,row_num;

select row_gid,row_name,row_num;

set i=i+1;

until i>row_count end repeat;

close myCursor;

end;

三、游标+continue handler实现遍历行：

continue handler 当fetch触发此handler后，后面的语句继续执行。
所以会多执行一次select row_gid,row_name,row_num;
此handler常用。

create procedure p15()

begin

declare row_gid int;
declare row_name varchar(20);
declare row_num int;
declare you int default 1;

declare myCursor cursor for select gid,name,num from goods;

declare continue handler for NOT FOUND set you=0;

open myCursor;

repeat

fetch myCursor into row_gid,row_name,row_num;

select row_gid,row_name,row_num;

until you=0 end repeat;

close myCursor;

end;

四、游标+loop实现遍历行：

-- loop 与 leave,iterate 实现循环
-- loop 标志位无条件循环；leave 类似于Java break 语句，跳出循环，即跳出 begin end；
iterate 类似于java continue ，结束本次循环，继续下一次循环。
--loop的优点在于可以根据条件结束本次循环或者根据条件跳出循环。

create procedure p17()

begin

declare row_gid int;
declare row_name varchar(20);
declare row_num int;
declare over int default 0;

declare myCursor cursor for select gid,name,num from goods;

declare continue handler for NOT FOUND set over=1;

open myCursor;

cursor_loop:loop

fetch myCursor into row_gid,row_name,row_num;

if over then

leave cursor_loop;

end if;

select row_gid,row_name,row_num;

end loop cursor_loop;

close myCursor;

end;

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