MySQL 游标

Posted 2023-02-20 落叶成冰

声明游标

declare CURSOR_NAME curosr for SELECT_STATEMENT;

打开游标

open CURSOR_NAME;

关闭游标

close CURSOR_NAME;

从游标中取数据

fetch CURSOR_NAME into var1, var2, ...;

示例1：

delimiter //
drop procedure if exists p//
create procedure p()
begin
	declare id int;
	declare name varchar(20);
	declare pass varchar(20);
	
	#声明游标
	declare cur_user cursor for select * from user;
	
	#打开游标
	open cur_user;
	
	#取数据
	fetch cur_user into id,name,pass;
	select id,name,pass;
	
	fetch cur_user into id,name,pass;
	select id,name,pass;
	
	fetch cur_user into id,name,pass;
	select id,name,pass;
	  
	#关闭游标
	close cur_user;
end//
delimiter ;

示例2：

delimiter //
drop procedure if exists p2//
create procedure p2()
begin
	declare id int;
	declare name varchar(20);
	declare pass varchar(20);

	# 记录总数
	declare num int;
	declare i int default 0;
	
	#声明游标
	declare cur_user cursor for select * from user;
	
	# 查询记录总数
	select count(*) into num from user;
	set i := 1;

	#打开游标
	open cur_user;
	
	#取数据
	repeat
		fetch cur_user into id,name,pass;
		select id,name,pass;
		set i := i + 1;
	until i>num end repeat;
	
	#关闭游标
	close cur_user;
end//
delimiter ;

示例3：

delimiter //
drop procedure if exists p3//
create procedure p3()
begin
	declare id int;
	declare name varchar(20);
	declare pass varchar(20);
	
	# has=1 表示还有数据
	declare has int default 1;
	
	#声明游标
	declare cur_user cursor for select * from user;

	# continue handler 触发后后面的语句急促执行
	# exit handler 触发后后面的语句不再执行
	# undo handler 触发后前面的语句撤销, 但是 mysql 不支持

	#声明 continue handler
	declare continue handler for NOT FOUND set has := 0;

	#打开游标
	open cur_user;

	#取数据
	repeat
		fetch cur_user into id,name,pass;
		select id,name,pass;
	until has=0 end repeat;

	#关闭游标
	close cur_user;
end//
delimiter ;

示例4：

delimiter //
drop procedure if exists p4//
create procedure p4()
begin
	declare id int;
	declare name varchar(20);
	declare pass varchar(20);
	
	# has=1 表示还有数据
	declare has int default 1;
	
	#声明游标
	declare cur_user cursor for select * from user;

	#声明 continue handler
	declare continue handler for NOT FOUND set has := 0;

	#打开游标
	open cur_user;

	fetch cur_user into id,name,pass;
	while has=1 do
		select id,name,pass;
		fetch cur_user into id,name,pass;
	end while;

	#关闭游标
	close cur_user;
end//
delimiter ;