深入学习mysql存储过程

Posted 2022-11-24 张文琪2022

这里的存储过程都是通过sql语句实现的，用来练习的表结构：

CREATE TABLE `test` (
  `id` varchar(10) NOT NULL,
  `name` varchar(50) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

代码一、基本结构

DROP PROCEDURE IF EXISTS test;#如存在同名存储过程则删除
CREATE PROCEDURE test()
BEGIN#开始标识
	declare _count int DEFAULT 0;
	#声明变量，建议变量名可用下划线开头不容易出错
	SELECT count(1) INTO _count FROM test;
	#查找数据并存入变量
	SELECT _count;#输出变量
END#结束标识

代码二：循环读取数据

DROP PROCEDURE IF EXISTS test;#dsad 
CREATE PROCEDURE test()
BEGIN
	declare done int default false;
	declare _id VARCHAR(10);
	declare _name VARCHAR(50);
	declare _cur cursor for (SELECT * FROM test);
	#声明游标变量
	declare continue HANDLER for not found set done = true;
	#更新退出循环条件
	open _cur;#打开游标
	loop1:loop#开始循环
	fetch _cur into _id,_name;#赋值
	if done then  #退出
	leave loop1; 
	end if;
	SELECT _id,_name;
	end loop loop1;
END

代码三：新增数据

DROP PROCEDURE IF EXISTS test;
CREATE PROCEDURE test(IN _id VARCHAR(10),IN _name VARCHAR(50))
BEGIN
	declare _count int DEFAULT 0;
	SELECT count(1) into _count FROM test WHERE ID = _id;
	IF _count <> 0 then
		SELECT "该ID已存在";
	ELSE 
		INSERT INTO test VALUES(_id,_name);
		COMMIT;
	END IF;

END

代码四：存储过程之间的调用（代码三的改编）

DROP PROCEDURE IF EXISTS _save; 
CREATE PROCEDURE _save(IN _id VARCHAR(10),IN _name VARCHAR(50))
BEGIN
		INSERT INTO test VALUES(_id,_name);
		COMMIT;
END



DROP PROCEDURE IF EXISTS test;
CREATE PROCEDURE test(IN _id VARCHAR(10),IN _name VARCHAR(50))
BEGIN
	declare _count int DEFAULT 0;
	SELECT count(1) into _count FROM test WHERE ID = _id;
	IF _count <> 0 then
		SELECT "该ID已存在";
	ELSE 
		CALL _save(_id,_name);
	END IF;

END