diff --git a/数据库系统原理与实践/平时作业/mypreamble.tex b/数据库系统原理与实践/平时作业/mypreamble.tex index a67d853..3f47a61 100644 --- a/数据库系统原理与实践/平时作业/mypreamble.tex +++ b/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} @@ -34,4 +37,109 @@ innertopmargin=10pt,linecolor=verificationColor,% linewidth=2pt,topline=true, % frametitleaboveskip=\dimexpr-\ht\strutbox\relax, -]{verification} \ No newline at end of file +]{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 \ No newline at end of file diff --git a/数据库系统原理与实践/平时作业/第三次作业.tex b/数据库系统原理与实践/平时作业/第三次作业.tex new file mode 100644 index 0000000..fff5cd2 --- /dev/null +++ b/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} \ No newline at end of file