class-notes/MySQL练习（一）.md at 53aacb1dee120f84fc794b34837467b48524eb7c

2025-02-27 17:28:52 +08:00

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第一套

#1 插入记录
/*
主键自增字段:DEFAULT
设置成空值:NULL
*/
INSERT INTO t_employee()
VALUES('e0013', '刘红', '女', 22, '实习生', 'd0002', NULL);
#2.修改表结构
/*
修改表中字段的数据类型
ALTER TABLE 表名 MODIFY 字段名 数据类型 [约束]; 
*/
ALTER TABLE t_employee MODIFY sex ENUM('男', '女');
#3 创建外键
/*
学生表(学号、姓名、班级编号)
班级表(班级编号、班级名称)
外键表：学生表 主键表：班级表
ALTER TABLE 学生表 ADD CONSTRAINT fk_st FOREIGN KEY(班级编号) REFERENCES 班级表(班级编号);

FOREIGN KEY(字段) 外键表中的字段
REFERENCES 表名(字段) 字段是表中的主键
*/
ALTER TABLE 表名 ADD CONSTRAINT 外键名 FOREIGN KEY(字段名) REFERENCES 表名(主键字段名);
ALTER TABLE t_employee ADD CONSTRAINT fK_did FOREIGN KEY(did) REFERENCES t_department(did);

#4 排序、分页查询 tj11
/*
基础查询
SELECT 字段
FROM 表
ORDER BY 需要排序的字段 ASC/DESC(升序/降序)
LIMIT 起始位置,个数;
*/
#查询出员工的所有信息
SELECT *
FROM t_employee;
#在基础查询之上对年龄进行降序排序
SELECT *
FROM t_employee
ORDER BY age DESC;
#在排序的基础之上，进行分页
SELECT *
FROM t_employee
ORDER BY age DESC
LIMIT 5, 8;#第0个代表第一个 第六个使用的位置是5

#5条件查询 tj12
/*
SELECT 字段
FROM 表
WHERE 条件;
*/
SELECT *
FROM t_salary
WHERE money >= 5000 AND money <= 8000;

#6 tj13 分组查询
SELECT eid, MAX(money)
FROM t_salary
GROUP BY eid;

#7 tj14 多表联查+条件过滤
SELECT d.dname, e.ename
FROM t_employee e, t_department d
WHERE e.did = d.did AND e.position = '经理';

#8
CREATE VIEW v_hrm AS
SELECT d.dname, e.ename, s.money, s.stime
FROM t_employee e, t_department d, t_salary s
WHERE e.did = d.did AND e.eid = s.eid
ORDER BY s.stime DESC;

#9 触发器
DELIMITER $$
DROP TRIGGER IF EXISTS tri_updateGroup;
CREATE TRIGGER tri_updateGroup
BEFORE UPDATE ON t_employee
FOR EACH ROW
BEGIN
	IF NEW.age != OLD.age THEN
		IF NEW.age<30 THEN
			SET NEW.groups = '青年';
		ELSEIF NEW.age<50 THEN
			SET NEW.groups = '中年';
		ELSE
			SET NEW.groups = '老年';
		END IF;
	END IF;
END $$
DELIMITER ;

#10 存储过程
DELIMITER $$ #改变代码结束符
DROP PROCEDURE IF EXISTS pro_GetTopSalary;#创建存储过程之前先删除
#设置存储过程名，传入传出参数名和数据类型
CREATE PROCEDURE pro_GetTopSalary(IN in_did CHAR(10), OUT out_ename VARCHAR(30))
BEGIN
	#连接查询+排序+分页
	SELECT e.ename INTO out_ename
	FROM t_employee e, t_salary s
	WHERE e.eid = s.eid AND e.did = in_did
	ORDER BY s.money DESC
	LIMIT 1;
END $$
DELIMITER ;
#调用存储过程 传入用户变量接收传出数据并使用打印出来
CALL pro_GetTopSalary('d0001', @result);
SELECT @result;

第二套

#1 创建表
CREATE TABLE t_booking(
	bid CHAR(10) PRIMARY KEY,
	rid CHAR(10) NOT NULL,
	customerName VARCHAR(50),
	tel VARCHAR(30),
	btime DATE
);

#2 插入记录
INSERT INTO t_booking()
VALUES('b0001', 'r0002', '诸葛亮', '1821234567', '2023-10-01');

#3 添加字段
ALTER TABLE t_hotel ADD introduce VARCHAR(255);

#4 更新记录
UPDATE t_room r
SET r.price = 500
WHERE r.rid = 'r0003';

#5 tj11
SELECT *
FROM t_hotel h
WHERE h.`level` IN ('二星', '三星');

#6 tj12
SELECT h.hid, ROUND(AVG(r.price), 2)
FROM t_hotel h, t_room r
WHERE h.hid = r.hid
GROUP BY h.hid;

#7 子查询 + 视图
CREATE VIEW v_hotel AS
SELECT h.hname, r.rname, r.price
FROM t_hotel h, t_room r
WHERE h.hid = r.hid AND r.price =(
	SELECT MAX(price)
	FROM t_room
	WHERE hid = h.hid
);

#8 触发器
DELIMITER $$
DROP TRIGGER IF EXISTS tri_updateIntroduce;
CREATE TRIGGER tri_updateIntroduce
BEFORE UPDATE ON t_hotel
FOR EACH ROW
BEGIN
		IF NEW.`level` = '一星' OR NEW.`level` = '二星' THEN
			SET NEW.introduce = '实用';
		ELSEIF NEW.`level` = '三星' OR  NEW.`level` = '四星' THEN
			SET NEW.introduce = '豪华';
		ELSEIF NEW.`level` = '五星' THEN
			SET NEW.introduce = '奢华';
		END IF;
END $$
DELIMITER ;

#9 存储过程
DELIMITER $$
DROP PROCEDURE IF EXISTS pro_GetLowPrice;
CREATE PROCEDURE pro_GetLowPrice(IN in_rname VARCHAR(30), OUT out_hname VARCHAR(30))
BEGIN
	SELECT h.hname INTO out_hname
	FROM t_hotel h, t_room r
	WHERE h.hid = r.hid AND r.rname = in_rname
	ORDER BY r.price
	LIMIT 1;
END $$
DELIMITER ;

CALL pro_GetLowPrice('标准间', @result);
SELECT @result;

第三套

#1
CREATE TABLE tb_order(
	oid INT PRIMARY KEY AUTO_INCREMENT COMMENT '订单ID',
	odate DATETIME NOT NULL COMMENT '下单日期',
	quantity INT NOT NULL DEFAULT 1 COMMENT '下单数量'
);

#2
ALTER TABLE tb_books MODIFY price DECIMAL(10, 2);

#3
ALTER TABLE tb_book_authors ADD CONSTRAINT tB_ibfk_1 FOREIGN KEY(book_id) REFERENCES tb_books(book_id);

ALTER TABLE tb_book_authors ADD CONSTRAINT tB_ibfk_2 FOREIGN KEY(author_id) REFERENCES tb_authors(author_id);

#4
ALTER TABLE tb_authors ADD avatar MEDIUMBLOB;

#5
#使用查询和LOAD_FILE函数 导入指定路径的图片
SELECT LOAD_FILE('C:/TTLXExam/20501071168/MYSQLDB/3/jinyong.jpg');

UPDATE tb_authors a
SET a.avatar = LOAD_FILE('C:/TTLXExam/20501071168/MYSQLDB/3/jinyong.jpg')
WHERE a.author_name = '金庸';

#6
#INSTR(主串, 子串) 判断子串在主串中的位置并返回
#SUBSTR(字符串, 起始位置) 从起始位置开始截取字符串
SELECT SUBSTR(b.note,INSTR(b.note,'-')+2)
FROM tb_books b;

UPDATE tb_books b
SET b.note = SUBSTR(b.note,INSTR(b.note,'-')+2);

#7 tj11 多表连接+条件+排序
SELECT b.book_id, b.title, a.author_id, a.author_name, b.publication_date
FROM tb_books b, tb_authors a
WHERE b.note = a.author_name  AND YEAR(b.publication_date) BETWEEN 1980 AND 2010
ORDER BY b.publication_date DESC;

#8 tj12 多表连接+分组+分组后条件
SELECT a.author_id, a.author_name, COUNT(*)
FROM tb_books b, tb_authors a
WHERE b.note = a.author_name
GROUP BY a.author_id
HAVING COUNT(*) > 1;


#9

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