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2207/天天乐学答案/MySQL练习（一）.md
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2207/天天乐学答案/MySQL练习（一）.md
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### 第一套
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```sql
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#1 插入记录
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/*
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主键自增字段:DEFAULT
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设置成空值:NULL
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*/
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INSERT INTO t_employee()
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VALUES('e0013', '刘红', '女', 22, '实习生', 'd0002', NULL);
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#2.修改表结构
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/*
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修改表中字段的数据类型
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ALTER TABLE 表名 MODIFY 字段名 数据类型 [约束];
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*/
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ALTER TABLE t_employee MODIFY sex ENUM('男', '女');
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#3 创建外键
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/*
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学生表(学号、姓名、班级编号)
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班级表(班级编号、班级名称)
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外键表：学生表 主键表：班级表
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ALTER TABLE 学生表 ADD CONSTRAINT fk_st FOREIGN KEY(班级编号) REFERENCES 班级表(班级编号);
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FOREIGN KEY(字段) 外键表中的字段
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REFERENCES 表名(字段) 字段是表中的主键
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*/
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ALTER TABLE 表名 ADD CONSTRAINT 外键名 FOREIGN KEY(字段名) REFERENCES 表名(主键字段名);
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ALTER TABLE t_employee ADD CONSTRAINT fK_did FOREIGN KEY(did) REFERENCES t_department(did);
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#4 排序、分页查询 tj11
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/*
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基础查询
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SELECT 字段
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FROM 表
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ORDER BY 需要排序的字段 ASC/DESC(升序/降序)
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LIMIT 起始位置,个数;
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*/
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#查询出员工的所有信息
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SELECT *
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FROM t_employee;
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#在基础查询之上对年龄进行降序排序
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SELECT *
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FROM t_employee
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ORDER BY age DESC;
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#在排序的基础之上，进行分页
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SELECT *
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FROM t_employee
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ORDER BY age DESC
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LIMIT 5, 8;#第0个代表第一个 第六个使用的位置是5
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#5条件查询 tj12
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/*
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SELECT 字段
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FROM 表
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WHERE 条件;
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*/
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SELECT *
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FROM t_salary
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WHERE money >= 5000 AND money <= 8000;
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#6 tj13 分组查询
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SELECT eid, MAX(money)
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FROM t_salary
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GROUP BY eid;
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#7 tj14 多表联查+条件过滤
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SELECT d.dname, e.ename
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FROM t_employee e, t_department d
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WHERE e.did = d.did AND e.position = '经理';
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#8
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CREATE VIEW v_hrm AS
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SELECT d.dname, e.ename, s.money, s.stime
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FROM t_employee e, t_department d, t_salary s
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WHERE e.did = d.did AND e.eid = s.eid
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ORDER BY s.stime DESC;
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#9 触发器
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DELIMITER $$
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DROP TRIGGER IF EXISTS tri_updateGroup;
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CREATE TRIGGER tri_updateGroup
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BEFORE UPDATE ON t_employee
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FOR EACH ROW
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BEGIN
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IF NEW.age != OLD.age THEN
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IF NEW.age<30 THEN
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SET NEW.groups = '青年';
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ELSEIF NEW.age<50 THEN
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SET NEW.groups = '中年';
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ELSE
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SET NEW.groups = '老年';
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END IF;
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END IF;
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END $$
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DELIMITER ;
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#10 存储过程
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DELIMITER $$ #改变代码结束符
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DROP PROCEDURE IF EXISTS pro_GetTopSalary;#创建存储过程之前先删除
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#设置存储过程名，传入传出参数名和数据类型
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CREATE PROCEDURE pro_GetTopSalary(IN in_did CHAR(10), OUT out_ename VARCHAR(30))
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BEGIN
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#连接查询+排序+分页
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SELECT e.ename INTO out_ename
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FROM t_employee e, t_salary s
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WHERE e.eid = s.eid AND e.did = in_did
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ORDER BY s.money DESC
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LIMIT 1;
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END $$
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DELIMITER ;
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#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
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CALL pro_GetTopSalary('d0001', @result);
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SELECT @result;
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```
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### 第二套
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```sql
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#1 创建表
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CREATE TABLE t_booking(
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bid CHAR(10) PRIMARY KEY,
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rid CHAR(10) NOT NULL,
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customerName VARCHAR(50),
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tel VARCHAR(30),
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btime DATE
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);
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#2 插入记录
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INSERT INTO t_booking()
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VALUES('b0001', 'r0002', '诸葛亮', '1821234567', '2023-10-01');
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#3 添加字段
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ALTER TABLE t_hotel ADD introduce VARCHAR(255);
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#4 更新记录
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UPDATE t_room r
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SET r.price = 500
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WHERE r.rid = 'r0003';
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#5 tj11
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SELECT *
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FROM t_hotel h
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WHERE h.`level` IN ('二星', '三星');
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#6 tj12
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SELECT h.hid, ROUND(AVG(r.price), 2)
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FROM t_hotel h, t_room r
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WHERE h.hid = r.hid
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GROUP BY h.hid;
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#7 子查询 + 视图
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CREATE VIEW v_hotel AS
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SELECT h.hname, r.rname, r.price
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FROM t_hotel h, t_room r
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WHERE h.hid = r.hid AND r.price =(
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SELECT MAX(price)
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FROM t_room
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WHERE hid = h.hid
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);
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#8 触发器
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DELIMITER $$
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DROP TRIGGER IF EXISTS tri_updateIntroduce;
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CREATE TRIGGER tri_updateIntroduce
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BEFORE UPDATE ON t_hotel
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FOR EACH ROW
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BEGIN
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IF NEW.`level` = '一星' OR NEW.`level` = '二星' THEN
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SET NEW.introduce = '实用';
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ELSEIF NEW.`level` = '三星' OR NEW.`level` = '四星' THEN
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SET NEW.introduce = '豪华';
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ELSEIF NEW.`level` = '五星' THEN
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SET NEW.introduce = '奢华';
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END IF;
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END $$
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DELIMITER ;
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#9 存储过程
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DELIMITER $$
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DROP PROCEDURE IF EXISTS pro_GetLowPrice;
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CREATE PROCEDURE pro_GetLowPrice(IN in_rname VARCHAR(30), OUT out_hname VARCHAR(30))
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BEGIN
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SELECT h.hname INTO out_hname
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FROM t_hotel h, t_room r
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WHERE h.hid = r.hid AND r.rname = in_rname
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ORDER BY r.price
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LIMIT 1;
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END $$
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DELIMITER ;
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CALL pro_GetLowPrice('标准间', @result);
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SELECT @result;
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```
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### 第三套
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```sql
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#1
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CREATE TABLE tb_order(
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oid INT PRIMARY KEY AUTO_INCREMENT COMMENT '订单ID',
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odate DATETIME NOT NULL COMMENT '下单日期',
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quantity INT NOT NULL DEFAULT 1 COMMENT '下单数量'
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);
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#2
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ALTER TABLE tb_books MODIFY price DECIMAL(10, 2);
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#3
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ALTER TABLE tb_book_authors ADD CONSTRAINT tB_ibfk_1 FOREIGN KEY(book_id) REFERENCES tb_books(book_id);
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ALTER TABLE tb_book_authors ADD CONSTRAINT tB_ibfk_2 FOREIGN KEY(author_id) REFERENCES tb_authors(author_id);
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#4
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ALTER TABLE tb_authors ADD avatar MEDIUMBLOB;
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#5
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#使用查询和LOAD_FILE函数 导入指定路径的图片
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SELECT LOAD_FILE('C:/TTLXExam/20501071168/MYSQLDB/3/jinyong.jpg');
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UPDATE tb_authors a
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SET a.avatar = LOAD_FILE('C:/TTLXExam/20501071168/MYSQLDB/3/jinyong.jpg')
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WHERE a.author_name = '金庸';
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#6
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#INSTR(主串, 子串) 判断子串在主串中的位置并返回
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#SUBSTR(字符串, 起始位置) 从起始位置开始截取字符串
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SELECT SUBSTR(b.note,INSTR(b.note,'-')+2)
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FROM tb_books b;
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UPDATE tb_books b
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SET b.note = SUBSTR(b.note,INSTR(b.note,'-')+2);
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#7 tj11 多表连接+条件+排序
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SELECT b.book_id, b.title, a.author_id, a.author_name, b.publication_date
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FROM tb_books b, tb_authors a
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WHERE b.note = a.author_name AND YEAR(b.publication_date) BETWEEN 1980 AND 2010
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ORDER BY b.publication_date DESC;
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#8 tj12 多表连接+分组+分组后条件
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SELECT a.author_id, a.author_name, COUNT(*)
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FROM tb_books b, tb_authors a
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WHERE b.note = a.author_name
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GROUP BY a.author_id
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HAVING COUNT(*) > 1;
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#9 视图
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CREATE VIEW v_book AS
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SELECT b.genre, a.author_name, COUNT(*) c
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FROM tb_books b, tb_authors a
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WHERE b.note = a.author_name
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GROUP BY b.genre, a.author_id #按照图书类别和作者名称进行分组
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HAVING COUNT(*) = ( #子查询用来统计这个类别中 数量最多的作者的图书数量
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SELECT COUNT(*)
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FROM tb_books
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WHERE b.genre = genre
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GROUP BY note
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ORDER BY COUNT(*) DESC
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LIMIT 1
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);
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#10 触发器
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DELIMITER $$
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DROP TRIGGER IF EXISTS tri_updateCentury;
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CREATE TRIGGER tri_updateCentury
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BEFORE UPDATE ON tb_books
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FOR EACH ROW
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BEGIN
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#方式一
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/*
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计算出世纪数+字符串拼接
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IF NEW.publication_date <> OLD.publication_date THEN
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SET NEW.century = CONCAT(FLOOR(YEAR(NEW.publication_date)/100) + 1, '世纪');
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END IF;
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*/
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#方式二 使用多分支IF
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IF NEW.publication_date <> OLD.publication_date THEN
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IF YEAR(NEW.publication_date) BETWEEN 1800 AND 1899 THEN
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SET NEW.century = '19世纪';
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ELSEIF YEAR(NEW.publication_date) BETWEEN 1900 AND 1999 THEN
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SET NEW.century = '20世纪';
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ELSEIF YEAR(NEW.publication_date) BETWEEN 2000 AND 2099 THEN
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SET NEW.century = '21世纪';
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END IF;
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END IF;
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END $$
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DELIMITER ;
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SELECT CONCAT(FLOOR(YEAR(publication_date)/100) + 1, '世纪')
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FROM tb_books;
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#11 存储过程
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DELIMITER $$
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DROP PROCEDURE IF EXISTS pro_GetTopFictionPrice;
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CREATE PROCEDURE pro_GetTopFictionPrice(IN in_genre VARCHAR(255), OUT out_title VARCHAR(255))
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BEGIN
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SELECT b.title INTO out_title
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FROM tb_books b
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WHERE b.genre = in_genre AND YEAR(b.publication_date) BETWEEN 2000 AND 2099
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ORDER BY b.price DESC
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LIMIT 1;
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END $$
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DELIMITER ;
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```
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### 第四套
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```sql
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#1
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ALTER TABLE tb_students MODIFY gender ENUM('男', '女', '未知');
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#2
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ALTER TABLE tb_scores MODIFY score FLOAT(7, 2);
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#3
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CREATE TABLE tb_scores_bak1 AS
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SELECT *
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FROM tb_scores;
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#4
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UPDATE test1 t1, (
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SELECT tname, CONCAT(tname,'@',COUNT(*)) str
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FROM test1
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GROUP BY tname
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HAVING COUNT(*) IN (3, 4)
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)t2
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SET t1.tname = t2.str
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WHERE t1.tname = t2.tname;
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#5
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SELECT *
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FROM tb_courses c
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ORDER BY c.cid+0
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LIMIT 4, 11;
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#6
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SELECT s.stuname, TIMESTAMPDIFF(YEAR,s.birthday,'2023-12-01')
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FROM tb_students s
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WHERE TIMESTAMPDIFF(YEAR,s.birthday,'2023-12-01') BETWEEN 30 AND 40;
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#7
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#8
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```
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