527 lines
17 KiB
TeX
527 lines
17 KiB
TeX
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\documentclass[全部作业]{subfiles}
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\input{mysubpreamble}
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% 不知道为什么这里又变成不用framed才能不出现换页问题了
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% \BeforeBeginEnvironment{minted}{}
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% \AfterEndEnvironment{minted}{}
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% 这样好像不能替换掉原来的，那就只能把framed移动到需要的部分里了
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\begin{document}
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\setcounter{chapter}{5}
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\chapter{第六次作业}
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\begin{enumerate}
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\item \choice[1]{关于游标，选项中说法错误的是（）
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A
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游标可以定在查询结果集的特定行，也可以从结果集的当前行检索一行或多行
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B
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通常我们并不使用游标，但是需要逐条处理数据的时候，游标显得十分重要
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C
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游标使用时必须在完成后关闭，以释放资源
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D
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游标的 SELECT 语句中可以使用 INTO 子句来创建新表
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}{4}
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\item \choice[1]{下列关于触发器的描述正确的是（）
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A
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MySql的触发器只支持行级出发，不支持语句级触发
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B
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触发器可以调用将数据返回客户端的存储程序
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C
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在触发器中可以使用显式或者隐式方式开始或结束事务的语句
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D
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在MySql中，不可使用new和old引用触发器中发生的记录内容
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}{1}
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\item \choice[1]{关于before和after触发器的说法中，哪一项是正确的？（）
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A
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在 BEFORE 触发器中，可以对 INSERT 和 UPDATE 的 NEW 值进行修改；而在 AFTER 触发器中，无法修改 NEW 值
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B
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在 AFTER 触发器中，可以修改 NEW 值，但在 BEFORE 触发器中不能修改
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C
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BEFORE 触发器不能用于 UPDATE 操作
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D
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AFTER 触发器可以对 INSERT 和 UPDATE 的 NEW 值进行修改
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}{1}
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\item \choice[1]{关于 MySQL 触发器中 SELECT 语句的使用，以下哪种说法是正确的？（）
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A
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触发器中可以包含 SELECT 语句，并且可以返回结果集
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B
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触发器中可以包含 SELECT 语句，但不能返回结果集
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C
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触发器中必须包含 SELECT 语句，以便执行其他操作
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D
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触发器中可以使用 SELECT 语句来更新表的记录
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}{2}
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\item \choice[1]{关于存储过程的说法中，哪一项是正确的？（）
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A
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存储过程可以通过 SELECT 语句直接返回结果集给调用者
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B
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存储过程只能接受一个输入参数，并且不能返回任何值
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C
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存储过程可以使用 BEGIN ... END 块来定义多个 SQL 语句的执行逻辑
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D
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存储过程的定义必须包含 CREATE FUNCTION 关键字
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}{3}
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\questionandanswer[]{
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创建一个名为 check_student_age_trigger 的触发器，该触发器用于在 students 表中插入新记录之前进行年龄检查。要求如下：
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触发器在执行 INSERT 操作之前触发。
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如果新插入的学生年龄（age 列）小于 18 岁，触发器应该将 age 设置为 18。
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如果新插入的学生年龄大于 120 岁，触发器应该将 age 设置为 120。
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触发器应该记录所有插入操作的原始年龄值到一个名为 age_log 的表中，表结构如下：
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log_id: INT, 主键，自增
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student_id: INT, 学生学号
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original_age: INT，原始年龄值
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log_time: DATETIME，记录插入的时间
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要求：
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（1）编写 SQL 语句创建 age_log 表。
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（2）编写 SQL 语句创建 check_student_age_trigger 触发器。
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提示：
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使用 NEW 关键字访问将要插入的记录中的字段。
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使用 INSERT INTO 语句将原始年龄记录到 age_log 表中。
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示例：
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如果插入一条记录：INSERT INTO students (name, age) VALUES ('Alice', 16);
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触发器将插入 age 为 18，并在 age_log 表中记录 original_age 为 16。
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}{}
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{\kaishu
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\begin{minted}{SQL}
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create table age_log
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(
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log_id int primary key auto_increment,
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student_id int comment '学生学号',
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original_age int comment '原始年龄值',
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log_time datetime comment '记录插入的时间'
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);
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create trigger check_student_age_trigger
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before insert
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on students
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for each row
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begin
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insert into age_log(student_id, original_age, log_time) value (new.id, new.age, now());
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case
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when (new.age < 18) then set new.age = 18;
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when (new.age > 120) then set new.age = 120;
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end case;
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end;
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\end{minted}
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}
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\begin{verification}
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{\small
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\begin{minted}{SQL}
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drop table if exists students;
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drop table if exists age_log;
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create table students
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(
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id int primary key,
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name varchar(100) comment '姓名',
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age int comment '年龄'
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);
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create table age_log
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(
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log_id int primary key auto_increment,
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student_id int comment '学生学号',
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original_age int comment '原始年龄值',
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log_time datetime comment '记录插入的时间'
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);
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create trigger check_student_age_trigger
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before insert
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on students
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for each row
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begin
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insert into age_log(student_id, original_age, log_time) value (new.id, new.age, now());
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case
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when (new.age < 18) then set new.age = 18;
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when (new.age > 120) then set new.age = 120;
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end case;
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end;
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insert into students(id, name, age)
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values (10001, 'Alice', 16),
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(10002, 'Bob', 150);
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\end{minted}
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}
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students:
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\begin{csv}
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,id,name,age
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1,10001,Alice,18
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2,10002,Bob,120
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\end{csv}
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age_log:
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\begin{csv}
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,log_id,student_id,original_age,log_time
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1,1,10001,16,2024-11-01 15:39:52
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2,2,10002,150,2024-11-01 15:39:52
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\end{csv}
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\end{verification}
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\questionandanswer[]{
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假设有以下两个表：
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\noindent\includegraphics[width=1\linewidth]{imgs/2024-11-01-16-47-16.png}
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创建一个名为 withdraw_funds 的存储过程，用于从银行账户中提款。要求如下：
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存储过程接受两个参数：
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account_id: INT, 要提款的账户的 ID
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amount: DECIMAL(10, 2), 要提款的金额
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在提款前检查该账户的余额是否足够支付提款金额。
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如果余额不足，存储过程应返回一个错误消息。
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如果提款成功，更新账户余额，并在 transactions 表中记录提款信息（转出账户为提款账户，转入账户为 NULL，金额为提款金额）。
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}{}
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{\kaishu
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\begin{minted}{SQL}
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create procedure withdraw_funds(in _account_id int, in amount decimal(10, 2))
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begin
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start transaction;
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-- 如果账户不存在呢？好像没有交代应该怎么处理
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if (select accounts.balance from accounts where accounts.account_id = _account_id) < amount then
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rollback ;
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signal sqlstate '45000' set message_text = '余额不足';
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end if;
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update accounts set balance = balance - amount where accounts.account_id = _account_id;
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insert into transactions(from_account_id, to_account_id, amount) value (_account_id, null, amount);
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commit;
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end;
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\end{minted}
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}
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\begin{verification}
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{\small
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\begin{minted}{SQL}
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drop table if exists accounts;
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drop table if exists transactions;
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create table accounts
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(
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-- 自增好像是从1开始的
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account_id int primary key auto_increment comment '账户唯一标识符',
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account_holder varchar(100) comment '账户持有者的姓名',
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balance decimal(10, 2) comment '账户余额'
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);
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create table transactions
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(
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transaction_id int primary key auto_increment comment '交易的唯一标识符',
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from_account_id int comment '转出账户的ID',
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to_account_id int comment '转入账户的ID',
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amount decimal(10, 2) comment '转账金额',
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transaction_time datetime default current_timestamp comment '转账时间'
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);
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insert into accounts(account_holder, balance)
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values ('a', 10),
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('b', 100);
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drop procedure if exists withdraw_funds;
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create procedure withdraw_funds(in _account_id int, in amount decimal(10, 2))
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begin
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start transaction;
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-- 如果账户不存在呢？好像没有交代应该怎么处理
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if (select accounts.balance from accounts where accounts.account_id = _account_id) < amount then
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rollback ;
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signal sqlstate '45000' set message_text = '余额不足';
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end if;
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update accounts set balance = balance - amount where accounts.account_id = _account_id;
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insert into transactions(from_account_id, to_account_id, amount) value (_account_id, null, amount);
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commit;
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end;
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call withdraw_funds(2, 10);
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call withdraw_funds(1, 10);
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call withdraw_funds(1, 10);
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\end{minted}
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}
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\begin{minted}{text}
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[2024-11-01 16:35:33] [45000][1644] 余额不足
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\end{minted}
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accounts:
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\begin{csv}
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,account_id,account_holder,balance
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1,1,a,0.00
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2,2,b,90.00
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\end{csv}
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\vspace{1em}
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transactions:\vspace{1em}\\
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\small\begin{csv}
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,transaction_id,from_account_id,to_account_id,amount,transaction_time
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1,1,2,,10.00,2024-11-01 16:35:33
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2,2,1,,10.00,2024-11-01 16:35:34
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\end{csv}
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\end{verification}
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\questionandanswer[]{
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请根据下图所示的银行数据库，编写一个触发器来执行下列操作：在删除一个账户时，检查该账户的拥有者是否还有其他账户，如果没有，则将其从depositor关系中删除。
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\includegraphics[width=1\linewidth]{imgs/2024-11-01-21-57-55.png}
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}{}
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{\kaishu
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这里为什么要检测是否有其他账户，删除一个账户时不管这个人有没有其他账户都需要从depositor里删除account_number对应的行吧，那删除最后一个账户时depositor里自然也删完了。
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\begin{minted}{SQL}
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create trigger delete_account
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after delete
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on account
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for each row
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begin
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delete from depositor where account_number = old.account_number;
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end;
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\end{minted}
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}
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\begin{verification}
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\begin{minted}{SQL}
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drop table if exists account;
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drop table if exists depositor;
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create table account
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(
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account_number int primary key,
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branch_name varchar(100),
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balance int
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);
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create table depositor
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(
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customer_name varchar(100),
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account_number int references account.account_number
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);
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insert into account
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values (1, 'a', 100),
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(2, 'b', 200);
|
|||
|
|
|
|||
|
|
insert into depositor
|
|||
|
|
values ('c', 1),
|
|||
|
|
('c', 2);
|
|||
|
|
|
|||
|
|
create trigger delete_account
|
|||
|
|
after delete
|
|||
|
|
on account
|
|||
|
|
for each row
|
|||
|
|
begin
|
|||
|
|
delete from depositor where account_number = old.account_number;
|
|||
|
|
end;
|
|||
|
|
|
|||
|
|
delete from account where account_number = 1;
|
|||
|
|
select * from depositor;
|
|||
|
|
\end{minted}
|
|||
|
|
\begin{csv}
|
|||
|
|
,customer_name,account_number
|
|||
|
|
1,c,2
|
|||
|
|
\end{csv}
|
|||
|
|
\begin{minted}{SQL}
|
|||
|
|
delete from account where account_number = 2;
|
|||
|
|
select * from depositor;
|
|||
|
|
\end{minted}
|
|||
|
|
\begin{csv}
|
|||
|
|
,customer_name,account_number
|
|||
|
|
,,
|
|||
|
|
\end{csv}
|
|||
|
|
\end{verification}
|
|||
|
|
|
|||
|
|
\questionandanswer[]{
|
|||
|
|
假设有一个名为 employees 的员工表和一个名为 departments 的部门表，结构如下：
|
|||
|
|
\includegraphics[width=1\linewidth]{imgs/2024-11-02-11-15-08.png}
|
|||
|
|
（1）存储过程：名为 increase_salary，用于根据部门名称增加员工工资。要求：
|
|||
|
|
|
|||
|
|
接受两个参数：dept_name（部门名称）和 percentage（增加的百分比）。
|
|||
|
|
|
|||
|
|
如果部门不存在，返回错误消息。
|
|||
|
|
|
|||
|
|
如果部门存在，更新该部门所有员工的工资，并返回更新的员工数量。
|
|||
|
|
|
|||
|
|
}{}
|
|||
|
|
{\kaishu
|
|||
|
|
\begin{minted}{SQL}
|
|||
|
|
create procedure increase_salary(in dept_name varchar(100), in percentage int)
|
|||
|
|
begin
|
|||
|
|
if (select count(*) from departments where dept_name = departments.department_name) <= 0 then
|
|||
|
|
signal sqlstate '45000' set message_text = '部门不存在';
|
|||
|
|
end if;
|
|||
|
|
update employees join departments using (department_id)
|
|||
|
|
set salary = salary * (1 + percentage / 100)
|
|||
|
|
where department_name = dept_name;
|
|||
|
|
-- 存储过程怎么返回更新的员工数量
|
|||
|
|
-- 30 ms 中有 2 行受到影响 返回的影响行数应该就能反映更新的员工数量了
|
|||
|
|
end;
|
|||
|
|
\end{minted}
|
|||
|
|
}
|
|||
|
|
\questionandanswer[]{
|
|||
|
|
（2）函数：名为 get_average_salary，用于获取指定部门的平均工资。要求：
|
|||
|
|
|
|||
|
|
接受一个参数：dept_id（部门 ID）。
|
|||
|
|
|
|||
|
|
返回该部门员工的平均工资，如果没有员工，则返回 0。
|
|||
|
|
}{}
|
|||
|
|
{\kaishu
|
|||
|
|
\begin{minted}{SQL}
|
|||
|
|
create function get_average_salary(dept_id int) returns decimal(10, 2)
|
|||
|
|
begin
|
|||
|
|
declare result decimal(10, 2);
|
|||
|
|
if (select count(*) from employees where department_id = dept_id) <= 0 then
|
|||
|
|
set result = 0;
|
|||
|
|
else
|
|||
|
|
select avg(employees.salary) into result from employees where department_id = dept_id;
|
|||
|
|
end if;
|
|||
|
|
return result;
|
|||
|
|
end;
|
|||
|
|
\end{minted}
|
|||
|
|
}
|
|||
|
|
\begin{verification}
|
|||
|
|
\begin{minted}{SQL}
|
|||
|
|
drop table if exists employees;
|
|||
|
|
drop table if exists departments;
|
|||
|
|
drop procedure if exists increase_salary;
|
|||
|
|
drop function if exists get_average_salary;
|
|||
|
|
|
|||
|
|
create table employees
|
|||
|
|
(
|
|||
|
|
employee_id int primary key auto_increment comment '员工唯一标识符',
|
|||
|
|
employee_name varchar(100) comment '员工姓名',
|
|||
|
|
department_id int comment '部门ID',
|
|||
|
|
salary decimal(10, 2) comment '员工工资'
|
|||
|
|
);
|
|||
|
|
create table departments
|
|||
|
|
(
|
|||
|
|
department_id int primary key auto_increment comment '部门唯一标识符',
|
|||
|
|
department_name varchar(100) comment '部门名称'
|
|||
|
|
);
|
|||
|
|
\end{minted}
|
|||
|
|
\quad
|
|||
|
|
% 大概知道了，只要在前一页结束前的位置加一个minted分段，并且在这个分段前面或后面存在一个字符，即使是空白的\quad 也可以，就不会出现分页异常的问题了
|
|||
|
|
\begin{minted}{SQL}
|
|||
|
|
create procedure increase_salary(in dept_name varchar(100), in percentage int)
|
|||
|
|
begin
|
|||
|
|
if (select count(*) from departments where dept_name = departments.department_name) <= 0 then
|
|||
|
|
signal sqlstate '45000' set message_text = '部门不存在';
|
|||
|
|
end if;
|
|||
|
|
update employees join departments using (department_id)
|
|||
|
|
set salary = salary * (1 + percentage / 100)
|
|||
|
|
where department_name = dept_name;
|
|||
|
|
-- 存储过程怎么返回更新的员工数量
|
|||
|
|
-- 30 ms 中有 2 行受到影响 返回的影响行数应该就能反映更新的员工数量了
|
|||
|
|
end;
|
|||
|
|
|
|||
|
|
create function get_average_salary(dept_id int) returns decimal(10, 2)
|
|||
|
|
begin
|
|||
|
|
declare result decimal(10, 2);
|
|||
|
|
if (select count(*) from employees where department_id = dept_id) <= 0 then
|
|||
|
|
set result = 0;
|
|||
|
|
else
|
|||
|
|
select avg(employees.salary) into result from employees where department_id = dept_id;
|
|||
|
|
end if;
|
|||
|
|
return result;
|
|||
|
|
end;
|
|||
|
|
|
|||
|
|
insert into departments
|
|||
|
|
values (101, 'aaa'),
|
|||
|
|
(102, 'bbb');
|
|||
|
|
|
|||
|
|
insert into employees(employee_name, department_id, salary)
|
|||
|
|
values ('a', 101, 10),
|
|||
|
|
('b', 101, 100),
|
|||
|
|
('c', 102, 1000);
|
|||
|
|
\end{minted}
|
|||
|
|
\begin{minted}{SQL}
|
|||
|
|
select get_average_salary(101);
|
|||
|
|
\end{minted}
|
|||
|
|
\begin{csv}
|
|||
|
|
,get_average_salary(101)
|
|||
|
|
1,55.00
|
|||
|
|
\end{csv}
|
|||
|
|
\begin{minted}{SQL}
|
|||
|
|
select get_average_salary(103);
|
|||
|
|
\end{minted}
|
|||
|
|
\begin{csv}
|
|||
|
|
,get_average_salary(103)
|
|||
|
|
1,0.00
|
|||
|
|
\end{csv}
|
|||
|
|
\begin{minted}{SQL}
|
|||
|
|
call increase_salary('aaa', 50);
|
|||
|
|
\end{minted}
|
|||
|
|
\begin{minted}{text}
|
|||
|
|
[2024-11-02 11:13:13] 30 ms 中有 2 行受到影响
|
|||
|
|
\end{minted}
|
|||
|
|
\begin{minted}{SQL}
|
|||
|
|
select * from employees;
|
|||
|
|
\end{minted}
|
|||
|
|
\begin{csv}
|
|||
|
|
,employee_id,employee_name,department_id,salary
|
|||
|
|
1,1,a,101,15.00
|
|||
|
|
2,2,b,101,150.00
|
|||
|
|
3,3,c,102,1000.00
|
|||
|
|
\end{csv}
|
|||
|
|
\begin{minted}{SQL}
|
|||
|
|
call increase_salary('ccc', 100);
|
|||
|
|
\end{minted}
|
|||
|
|
\begin{minted}{text}
|
|||
|
|
[2024-11-02 11:22:51] [45000][1644] 部门不存在
|
|||
|
|
\end{minted}
|
|||
|
|
\end{verification}
|
|||
|
|
|
|||
|
|
\questionandanswer[]{
|
|||
|
|
存储过程、函数和触发器的区别？
|
|||
|
|
}{
|
|||
|
|
存储过程不能使用return语句返回结果，只能通过传入参数设置为out来返回结果；而函数可以直接使用return语句返回结果。
|
|||
|
|
触发器没有传入参数也不能返回结果，只能通过old和new获取更新前后的值。
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
\questionandanswer[]{
|
|||
|
|
触发器的作用？Mysql表中允许有多少个触发器？
|
|||
|
|
}{
|
|||
|
|
触发器定义了一系列操作，这一系列操作称为触发程序，当触发事件发生时，触发程序会自动运行。
|
|||
|
|
触发器主要用于监视某个表的插入（insert）、更新（update）和删除（delete）等更新操作，这些操作可以分别激活该表的insert、update和delete类型的触发程序运行，从而实现数据的自动维护。
|
|||
|
|
|
|||
|
|
在5.7.2版本以前，同一个表不能创建两个相同触发时间、触发事件的触发程序，那么就是6个触发器：
|
|||
|
|
before insert、after insert、before update、after update、before delete、after delete。
|
|||
|
|
|
|||
|
|
在5.7.2版本之后没有此限制，那么对触发器的数量就没有限制了。
|
|||
|
|
}
|
|||
|
|
\end{enumerate}
|
|||
|
|
\end{document}
|