数据库系统原理与实践——第三次作业

数据库系统原理与实践/平时作业/mypreamble.tex

@@ -2,6 +2,9 @@
 \usepackage[framemethod=TikZ]{mdframed}
 % \usepackage[tikz]{bclogo}
 \usepackage{fontawesome5}
+\usepackage{underscore}
+\usepackage{booktabs}
+\usepackage[l3]{csvsimple}
 
 \usepackage{amssymb, amsfonts, amstext, amsmath, amsopn, amsthm}
 \usepackage{booktabs}
@@ -35,3 +38,108 @@
     linewidth=2pt,topline=true, %
     frametitleaboveskip=\dimexpr-\ht\strutbox\relax,
 ]{verification}
+
+\setminted{breaklines=true}
+
+% 将minted的外框修复为framed，修复换行的问题
+\setlength{\FrameRule}{0pt}
+\BeforeBeginEnvironment{minted}{\begin{framed}}
+\AfterEndEnvironment{minted}{\end{framed}}
+
+
+\ExplSyntaxOn
+% \debug_on:n {all}
+\newcommand{\choice}[3][4]{
+    \seq_clear:N \l_tmpa_seq
+    \tl_clear:N \l_tmpa_tl
+    % 这种情况还是re.split好用，search和findall都不好用
+    \regex_split:nnNT {[\c{par}\ ]+[A-Z]\ } {#2} \l_tmpa_seq {
+        \seq_pop_left:NN \l_tmpa_seq \l_tmpa_tl
+        \tl_put_right:Nn \l_tmpa_tl {\begin{tasks}[](#1)}
+            \seq_map_indexed_inline:Nn \l_tmpa_seq {
+                \tl_if_eq:nnTF {##1}{#3} {
+                    \tl_set:Nn \l_tmpb_tl {##2}
+                    % \tl_show:N \l_tmpb_tl
+                    \regex_replace_once:nnNTF {\c{mint}} {\c{mint}[frame=single]}\l_tmpb_tl {
+                        \tl_put_right:Nn \l_tmpa_tl {\task}
+                        \tl_put_right:No \l_tmpa_tl {\l_tmpb_tl}
+                    }{
+                        \tl_put_right:Nn \l_tmpa_tl {\task \fbox {##2}}
+                    }
+                } {
+                    \tl_put_right:Nn \l_tmpa_tl {\task ##2}
+                }
+            }
+            \tl_put_right:Nn \l_tmpa_tl {\end{tasks}}
+        % 唉弄半天还是这种好用，token list就直接手动插入，这就完全不用考虑在环境中的扩展了
+        \l_tmpa_tl
+    }
+}
+
+% https://zhuanlan.zhihu.com/p/557120394
+\tl_const:Nn \c_csv_blank_line { \par }
+
+\cs_set:Npn \__csv_read:nV #1#2 {
+
+    \ior_open:Nn \g_tmpa_ior {#1}
+    \int_gzero:N \g_tmpa_int
+    \tl_clear:N \g_tmpa_tl
+    \tl_clear:N \l_tmpa_tl
+    
+
+    \bool_until_do:nn {\ior_if_eof_p:N \g_tmpa_ior}{
+        \ior_get:NN \g_tmpa_ior \l_csv_line_tl
+        \int_gincr:N \g_tmpa_int    % 行计数
+        \tl_clear:N \g_tmpb_tl
+
+        \tl_if_eq:NNF \l_csv_line_tl \c_csv_blank_line % 判断空行
+        {
+            \seq_set_split:NnV \l_tmpa_seq {,} \l_csv_line_tl
+            \int_gzero:N \g_tmpb_int
+            \tl_gset:Nn \rownum {\int_use:N \g_tmpa_int} %行号接口
+            \seq_map_inline:Nn \l_tmpa_seq {
+                \int_gincr:N \g_tmpb_int    % 列计数
+                % 提供列接口
+                % \tl_gset:cn {col \int_to_roman:n \g_tmpb_int}{##1}
+                \int_compare:nNnTF \g_tmpb_int = 1 { % 判断首列
+                    \tl_put_right:Nn \g_tmpb_tl {##1}
+                }{
+                    \tl_put_right:Nn \g_tmpb_tl {& ##1}
+                }
+            }
+            \tl_put_right:Nn \g_tmpb_tl {\\} % 一行结束
+            \int_compare:nNnT \g_tmpa_int = 1 { % 判断首行
+                \tl_set:Nx \l_tmpa_tl {\prg_replicate:nn \g_tmpb_int c}
+                \tl_show:N \l_tmpa_tl
+                \tl_put_right:Nn \g_tmpa_tl {\begin{tabular}}
+                \tl_put_right:Nx \g_tmpa_tl {{\tl_use:N \l_tmpa_tl}}
+                \tl_put_right:Nn \g_tmpa_tl {\toprule}
+            }
+            \tl_show:N \g_tmpa_tl
+            \tl_put_right:Nx \g_tmpa_tl {\tl_use:N \g_tmpb_tl}
+            \int_compare:nNnT \g_tmpa_int = 1 {
+                \tl_put_right:Nn \g_tmpa_tl {\midrule}
+            }
+        }
+    }
+
+    \tl_put_right:Nn \g_tmpa_tl {\bottomrule \end{tabular}}
+    \tl_use:N \g_tmpa_tl
+
+    \ior_close:N \g_tmpa_ior
+}
+
+\newcommand{\readcsv}[2]{        % L2命令
+    \__csv_read:nV {#1}{#2}
+}
+
+\newenvironment{csv}{
+    \VerbatimEnvironment
+    \begin{VerbatimOut}[codes={\catcode`\^^I=12},firstline,lastline]{rawfile.csv}%
+}{
+    \end{VerbatimOut}%
+    % \readcsv {rawfile.csv}{}
+    \csvautotabular{rawfile.csv}
+}
+
+\ExplSyntaxOff

数据库系统原理与实践/平时作业/第三次作业.tex

@@ -0,0 +1,444 @@
+\documentclass[全部作业]{subfiles}
+\input{mysubpreamble}
+
+\begin{document}
+\setcounter{chapter}{2}
+\chapter{第三次作业}
+\begin{enumerate}
+    \item \choice[1]{在 SQL 中，如果在 SELECT 语句中使用了未被聚合的属性，那么这些属性必须如何处理？
+    A
+    它们可以随意出现，不需要在 GROUP BY 中列出
+    
+    
+    
+    B
+    它们必须在 GROUP BY 子句中出现
+    
+    
+    
+    C
+    它们可以出现在 HAVING 子句中，而不需要在 GROUP BY 中
+    
+    
+    
+    D
+    它们只能出现在 WHERE 子句中
+    
+    }{2}
+    \item \choice[1]{WHERE和HAVING子句的主要区别是什么？
+
+
+
+    A
+    WHERE 子句只能用于数值列，而 HAVING 子句可以用于所有类型的列
+    
+    
+    
+    B
+    WHERE 子句在数据分组之前过滤数据，而 HAVING 子句在数据分组之后过滤聚合结果
+    
+    
+    
+    C
+     HAVING 子句只能在没有 GROUP BY 的情况下使用，而 WHERE 子句可以在有 GROUP BY 的情况下使用
+    
+    
+    
+    D
+    WHERE 子句和 HAVING 子句的功能完全相同
+    
+    }{2}
+    \item \choice[1]{标量子查询的主要特征是什么？
+
+
+
+    A
+    返回多个行和多个列的结果
+    
+    
+    
+    B
+    返回一个单一的值，通常是一个属性的聚合结果
+    
+    
+    
+    C
+    只能在 INSERT 语句中使用
+    
+    
+    
+    D
+    只能用于 WHERE 子句中
+    
+    }{2}
+    \item \choice[1]{在MySQL中，为什么在执行插入操作之前先执行 SELECT FROM WHERE 查询非常重要？
+
+
+
+    A
+    以便查看表的结构和数据类型
+    
+    
+    
+    B
+    以确保要插入的数据不会导致主键或唯一性约束冲突
+    
+    
+    
+    C
+    以便快速获取插入操作的执行时间
+    
+    
+    
+    D
+    以便在插入后自动更新相关的其他表}{2}
+    \item \choice[1]{在 SQL 中，以下关于 EXISTS 和 NOT EXISTS 的描述哪项是正确的？
+
+
+
+    A
+    EXISTS 总是返回 TRUE，无论子查询是否返回结果。
+    
+    
+    
+    B
+    EXISTS r 为 TRUE 当且仅当子查询 r 返回至少一行结果
+    
+    
+    
+    C
+    NOT EXISTS r 为 TRUE 当且仅当子查询 r 返回至少一行结果。
+    
+    
+    
+    D
+    EXISTS 子查询可以返回多个列，但必须返回唯一的值。}{2}
+    \item \choice[1]{假设有两个表格，"employees" 和 "departments"，它们的结构如下。我们想要查询每个部门的员工人数。以下选项中，哪个是合适的嵌套子查询语句？
+    
+    \includegraphics[width=1\linewidth]{imgs/2024-10-03-23-33-32.png}
+    
+    A
+     \mint{SQL}|SELECT department_name, COUNT(*) FROM employees JOIN departments ON employees.department_id = departments.id;|
+    
+    
+    
+    B
+    \mint{SQL}|SELECT department_name, COUNT(*) FROM employees WHERE department_id = departments.id;|
+    
+    
+    
+    C
+    \mint{SQL}|SELECT department_name, (SELECT COUNT(*) FROM employees WHERE employees.department_id = departments.id) FROM departments;|
+    
+    
+    
+    D
+    \mint{SQL}|SELECT department_name, COUNT(*) FROM departments JOIN employees ON employees.department_id = departments.id;|
+    }{3}
+    \begin{verification}
+        \begin{minted}{SQL}
+drop table if exists employees, departments;
+
+create table employees(
+    id int auto_increment primary key ,
+    name varchar(10),
+    department_id varchar(10)
+);
+create table departments(
+    id int auto_increment primary key ,
+    department_name varchar(10)
+);
+
+insert into employees(name, department_id)
+values ('John', 1),
+       ('Alice', 1),
+       ('Tom', 2),
+       ('Lisa', 2),
+       ('Mike', 3);
+
+insert into departments(department_name)
+values ('HR'),
+       ('IT'),
+       ('Sales');
+
+SELECT department_name, (SELECT COUNT(*) FROM employees WHERE employees.department_id = departments.id) FROM departments;
+        \end{minted}
+        \begin{csv}
+,department_name,(SELECT ...)
+1,HR,2
+2,IT,2
+3,Sales,1
+        \end{csv}
+    \end{verification}
+    
+    \questionandanswer[]{
+        count(1)、count(*) 与 count(列名) 的区别？
+    }{
+        在执行效果上，count(1)和count(*)都会把空值算入结果，而count(列名)会忽略空值。
+    
+        在执行效率上，count(主键列名) > count(1) > count(非主键列名)。
+    }
+
+    \questionandanswer[]{
+        Mysql中exist和in的区别？
+    }{
+        参考
+        \url{https://blog.csdn.net/jinjiniao1/article/details/92666614}\\
+        \url{https://cloud.tencent.com/developer/article/1144244}\\
+        \url{https://cloud.tencent.com/developer/article/1144253}
+
+        那么可以考虑以下两条语句：
+        \mint{SQL}|select * from A where exists (select * from B where B.id = A.id);|
+        \mint{SQL}|select * from A where A.id in (select id from B);|
+
+        以下称A为内表，B为外表，两条语句中括号内的内容为子查询结果。
+
+        根据参考文章可知，exists语句的执行过程是先把内表的数据全部取出来，然后对每一条数据判断是否满足子查询的条件，只用到了子查询的索引；而in语句的执行过程是先将子查询结果查询出来，再和内表连接，用到了内表和外表的索引。
+        
+        所以当子查询结果的数据较多，外表的数据较少时，exists有Block嵌套循环优化（目前还不理解），查询效率更高；而子查询结果的数据较少，外表的数据较多时，in由于能用到外表的索引，所以效率更高。
+    }
+
+    \questionandanswer[]{
+        OrderItems 表示订单商品表，含有字段订单号：order_num，订单价格：item_price；Orders 表代表订单信息表，含有顾客 id：cust_id 和订单号：order_num。使用子查询，返回购买价格为 10 美元或以上产品的顾客列表，结果无需排序。
+        
+        \includegraphics[width=0.4\linewidth]{imgs/2024-10-04-09-59-11.png}
+        \includegraphics[width=0.4\linewidth]{imgs/2024-10-04-10-04-16.png}
+    }{}
+    {
+        \begin{minted}{SQL}
+select cust_id from Orders where order_num in (
+    select order_num from OrderItems where item_price >= 10
+);
+        \end{minted}
+    }
+    \begin{verification}
+        \begin{minted}{SQL}
+drop table if exists orderitems, orders;
+
+create table if not exists OrderItems
+(
+    order_num  varchar(10),
+    item_price int
+);
+insert into OrderItems
+values ('a1', 10),
+       ('a2', 1),
+       ('a2', 1),
+       ('a2', 1),
+       ('a4', 2),
+       ('a5', 5),
+       ('a2', 1),
+       ('a7', 7);
+
+create table if not exists Orders
+(
+    order_num varchar(10),
+    cust_id   varchar(10)
+);
+
+insert into Orders
+values ('a1', 'cust10'),
+       ('a2', 'cust1'),
+       ('a2', 'cust1'),
+       ('a4', 'cust2'),
+       ('a5', 'cust5'),
+       ('a2', 'cust4'),
+       ('a7', 'cust7');
+
+select cust_id
+from Orders
+where order_num in (select order_num
+                    from OrderItems
+                    where item_price >= 10);
+        \end{minted}
+
+        \begin{csv}
+            ,cust_id
+            1,cust10            
+        \end{csv}
+
+    \end{verification}
+
+    \questionandanswer[]{
+        表 OrderItems 代表订单商品信息表，prod_id 为产品 id；Orders 表代表订单表有 cust_id 代表顾客 id 和订单日期 order_date。编写SQL语句，使用子查询来确定哪些订单（在 OrderItems 中）购买了 prod_id 为 "BR01" 的产品，然后从 Orders 表中返回每个产品对应的顾客 ID（cust_id）和订单日期（order_date），按订购日期对结果进行升序排序。
+
+        \includegraphics[width=0.5\linewidth]{imgs/2024-10-04-10-27-04.png}
+    }{}
+    {\kaishu
+        由于要使用子查询，这里不考虑使用连接，使用exists和in可以分别写出如下SQL语句，其功能一样：
+        \begin{minted}{SQL}
+select cust_id, order_date from Orders where exists(
+    select * from OrderItems where prod_id='BR01' and Orders.order_num = OrderItems.order_num
+) order by order_date;
+
+select cust_id, order_date from Orders where order_num in (
+    select order_num from OrderItems where prod_id='BR01'
+) order by order_date;
+        \end{minted}
+    }
+    \begin{verification}
+        \begin{minted}{SQL}
+drop table if exists OrderItems;
+create table if not exists OrderItems(
+    prod_id varchar(10),
+    order_num varchar(10)
+);
+
+insert into OrderItems
+values ('BR01', 'a0001'),
+       ('BR01', 'a0002'),
+       ('BR02', 'a0003'),
+       ('BR02', 'a0013');
+
+drop table if exists Orders;
+create table if not exists Orders(
+    order_num varchar(10),
+    cust_id varchar(10),
+    order_date datetime
+);
+
+insert into Orders
+values ('a0001', 'cust10', '2022-01-01 00:00:00'),
+       ('a0002', 'cust1', '2022-01-01 00:01:00'),
+       ('a0003', 'cust1', '2022-01-02 00:00:00'),
+       ('a0013', 'cust2', '2022-01-01 00:20:00');
+        \end{minted}
+        以下三种不同语句分别使用exists、in和连接，可以得到相同结果。
+        \begin{minted}{SQL}
+select cust_id, order_date from Orders where exists(
+    select * from OrderItems where prod_id='BR01' and Orders.order_num = OrderItems.order_num
+) order by order_date;
+
+select cust_id, order_date from Orders where order_num in (
+    select order_num from OrderItems where prod_id='BR01'
+) order by order_date;
+
+select cust_id, order_date from Orders natural join OrderItems where prod_id='BR01' order by order_date;
+        \end{minted}
+        \begin{csv}
+,cust_id,order_date
+1,cust10,2022-01-01 00:00:00
+2,cust1,2022-01-01 00:01:00
+        \end{csv}
+    \end{verification}
+    \questionandanswer[]{
+        有一个顾客ID列表，其中包含他们已订购的总金额。OrderItems 表代表订单信息，OrderItems 表有订单号：order_num 和商品售出价格：item_price、商品数量：quantity。编写SQL语句，返回顾客 ID（Orders 表中的 cust_id），并使用子查询返回 total_ordered 每个顾客的订单总数，将结果按金额从大到小排序。
+
+        \includegraphics[width=0.5\linewidth]{imgs/2024-10-04-10-27-32.png}
+    }{
+        注意返回的是订单总数，但是要按照金额从大到小排序。
+    }
+    {
+        \begin{minted}{SQL}
+select cust_id, count(*) as total_ordered
+from Orders
+         join (select order_num, sum(item_price * quantity) as total
+               from OrderItems
+               group by order_num) as a on Orders.order_num = a.order_num
+group by cust_id
+order by sum(total) desc;
+        \end{minted}
+    }
+    \begin{verification}
+        \begin{minted}{SQL}
+drop table if exists orderitems, orders;
+
+create table OrderItems(
+    order_num varchar(10),
+    item_price int,
+    quantity int
+);
+create table Orders(
+    order_num varchar(10),
+    cust_id varchar(10)
+);
+
+insert into OrderItems
+values ('a0001', 10, 105),
+       ('a0002', 1,1100),
+       ('a0002', 1, 200),
+       ('a0013', 2, 1121),
+       ('a0003', 5, 10),
+       ('a0003', 1, 19),
+       ('a0003', 7, 5);
+
+insert into Orders
+values ('a0001', 'cust10'),
+       ('a0002', 'cust1'),
+       ('a0003', 'cust1'),
+       ('a0013', 'cust2');
+
+select cust_id, count(*) as total_ordered
+from Orders
+         join (select order_num, sum(item_price * quantity) as total
+               from OrderItems
+               group by order_num) as a on Orders.order_num = a.order_num
+group by cust_id
+order by sum(total) desc;        
+        \end{minted}
+        \begin{csv}
+,cust_id,total_ordered
+1,cust2,1
+2,cust1,2
+3,cust10,1
+        \end{csv}
+    \end{verification}
+    \questionandanswer[]{
+        Products 表中检索所有的产品名称：prod_name、产品 id：prod_id；OrderItems 代表订单商品表，订单产品：prod_id、售出数量：quantity。编写 SQL 语句，从 Products 表中检索所有的产品名称（prod_name），以及名为 quant_sold 的计算列，其中包含所售产品的总数（在 OrderItems 表上使用子查询和 SUM(quantity) 检索）。
+        
+        \includegraphics[width=0.4\linewidth]{imgs/2024-10-04-10-27-50.png}
+        \includegraphics[width=0.4\linewidth]{imgs/2024-10-04-10-28-03.png}
+    }{}
+    {\kaishu
+        \begin{minted}{SQL}
+select Products.prod_name, a.quant_sold as quant_sold
+from Products
+         natural join (select prod_id, sum(quantity) as quant_sold
+                       from OrderItems
+                       group by prod_id) as a;
+        \end{minted}
+    }
+    \begin{verification}
+        \begin{minted}{SQL}
+drop table if exists Products, OrderItems;
+
+create table Products (
+    prod_id varchar(10),
+    prod_name varchar(10)
+);
+create table OrderItems (
+    prod_id varchar(10),
+    quantity int
+);
+
+insert into Products
+values ('a0001', 'egg'),
+       ('a0002', 'sockets'),
+       ('a0013', 'coffee'),
+       ('a0003', 'cola');
+
+insert into OrderItems
+values ('a0001', 105),
+       ('a0002', 1100),
+       ('a0002', 200),
+       ('a0013', 1121),
+       ('a0003', 10),
+       ('a0003', 19),
+       ('a0003', 5);
+
+select Products.prod_name, a.quant_sold as quant_sold
+from Products
+         natural join (select prod_id, sum(quantity) as quant_sold
+                       from OrderItems
+                       group by prod_id) as a;
+        \end{minted}
+        \begin{csv}
+,prod_name,quant_sold
+1,egg,105
+2,sockets,1300
+3,coffee,1121
+4,cola,34
+        \end{csv}
+    \end{verification}
+\end{enumerate}
+\end{document}