Joyce' Blog

在伪代码中，每一条指令占一行(else if 例外)，指令后不跟任何符号，缩进表示程序中的分支结构
定义变量的语句不用写出来，但必须在注释中给出

某些指令或子任务可以用文字来叙述，例如，”设x是A中的最大项”，这里A是一个数组；或者”将x插入L中”，这里L是一个链表
算术表达式可以使用通常的算术运算符（+，-，*，/，以及表示幂的^）。逻辑表达式可以使用关系运算符=,≠,<,>,≤和≥，以及逻辑运算符与(and),或（or），非（not）。

赋值语句：a←b 。
这里a是变量、数组项，b是算术表达式、逻辑表达式或指针表达式。
变量交换：a<->b
goto语句导致转向具有指定标号的语句。

条件语句：

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if i=10
    then xxxx  //if 后面必定跟上then，else后面不用跟then
    elseif i=9 //elseif 要连在一起写,else 和 then 要对齐
        then xxxx
        yyyy
    else xxxx//else 跟在elseif 的 then 对齐

循环：while和for

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while time<10
    do  xxxxx                  //while后面必定要紧跟缩进的do
    xxxxx
    end

for var init to limit by incr do
    s
end

for i←0 to 10        //for、while、if 后面的条件语句都不用加括号
    do ...                 //for后面必定要紧跟缩进的do
    ...

exit语句可以在通常的结束条件满足之前，被用来结束while循环或者for循环的执行。exit导致转向到紧接在包含exit的（最内层）while或者for循环后面的一个语句。

return用来指出一个算法执行的终点；如果算法在最后一条指令之后结束，它通常是被省略的；它被用得最多的场合是检测到不合需要的条件时。return的后面可以紧接被括在引号的信息。

算法中的注释被括在/ /之中。诸如read和output之类的各种输入或者输出也在需要时被用到。

原文：https://blog.csdn.net/u010126059/article/details/51077514

DDL - Data Definition Language

CREATE (1) Table - define table name, attributes, types

​ (2) View - define user view of data

​ (3) Index - create index on nominated attributes

DROP (1) Table - delete table, attributes and values

​ (2) View - delete user view(s)

​ (3) Index - delete index, indexes

​ Some DBMS have an ALTER command to vary attribute characteristics.

键的声明

声明含单个属性的键：在属性后面加PRIMARY KEY 或 UNIQUE

指明为UNIQUE的属性，允许有空值，但不允许多个空值（除了SQL SERVER 以外的大型数据库都是允许 UNIQUE约束有多个空值的。）；指明为PRIMARY KEY 的属性不允许有空值。

声明含多个属性的键：单独作为表的一个元素。

PRIMARY KEY 仅有一个； UNIQUE 可以有多个。

外键

关键字：REFERENCES

含单个属性的外键：在属性后面加 REFERENCES \ (\)

含多个属性的外键：单独作为表的一个元素。FOREIGN KEY ( \ ) REFERENCES \ ( \ )

被参照的属性必须是其他表的PRIMARY KEY 或 UNIQUE

更新操作

例：

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CREATE TABLE Beers (
	name	CHAR(20) PRIMARY KEY,
	manf	CHAR(20) );
CREATE TABLE Sells (
	bar	CHAR(20),
	beer	CHAR(20),
	price	REAL,
	FOREIGN KEY(beer) REFERENCES 	Beers(name));

对Beers进行修改，会有三种情况：Default (Reject)，Cascade，Set NULL

其他

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CREATE TABLE Sells (
	bar   CHAR(20),
	beer  VARCHAR(20)  DEFAULT 'HouseBeer',
	price REAL	     NOT NULL,
	PRIMARY KEY (bar,beer)
 );
 
ALTER TABLE Bars ADD phone CHAR(16) DEFAULT 'unlisted';
ALTER TABLE Bars DROP COLUMN license;
ALTER TABLE Sells ADD CHECK(…);

DML - Data Manipulation Language

SQL Queries

重命名 SELECT name AS beer (“AS” could be omitted)

select语句中可加表达式：SELECT bar, beer, price*120 AS priceInYen

在每一行增加一个固定的值：SELECT drinker, ‘likes Bud’ AS whoLikesBud

当字符串中有单引号时，改成双引号：WHERE bar = ‘Joe’’s Bar’ AND beer = ‘Bud’;

=，<>，<，>，<=，>=

AND, OR, NOT

格式：Attribute LIKE pattern (或NOT LIKE)

% stands for any string

_ stands for any one character

空值（未知或不可用）

比较的三种结果： TRUE, FALSE, UNKNOWN，任何值与NULL比较，结果为UNKNOWN，where筛选语句只留下结果为TRUE的

•TRUE = 1, FALSE = 0, and UNKNOWN = ½.

•AND = MIN; OR = MAX, NOT(x) = 1-x

输出排序：

–ORDER BY \

–ASC (升序，默认值)，DESC (降序)

Multi-relation Queries

别名：FROM Beers b1, Beers b2

WHERE b1.manf = b2.manf AND b1.name < b2.name;

子查询

in / not in 会去重

例：已知关系模式 R(a,b)和 S(b,c):

Q1: SELECT a FROM R,S WHERE R.b=S.b;

Q2: SELECT a FROM R WHERE b IN (SELECT b FROM S);

Q1的结果总是包含Q2的结果

“EXISTS(relation)” is true if the relation is nonempty.

例：

Find the beers that are the unique beer by their manufacturer.

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SELECT  name
FROM    Beers b1
WHERE NOT EXISTS  (SELECT * FROM    Beers
WHERE manf = b1.manf AND name <> b1.name);

x = ANY( \ ) is true if and only if x equals at least one tuple in the relation.

–That is, x is a member of the relation (x IN \)

等号可以被替换：x > ANY(\ ) means x is larger than at least one tuple in the relation.

–Note tuples must have one component only.

x <> ALL( \ ) is true if and only if for every tuple t in the relation, x is not equal to t.

–That is, x is not a member of the relation (x NOT IN \).

<>可以被替换

•x >= ALL( \ ) means there is no tuple larger than x in the relation.

–Note tuples must have one component only.

例：选择出预算最小的项目

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select projectname
from project
where budget<=ALL (select budget from project)

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SELECT 	drinker, AVG(price) FROM Frequents, Sells
WHERE  	beer = 'Bud' AND Frequents.bar = Sells.bar
GROUP BY drinker;

Find the average price of those beers that are either served in at least 3 bars or manufactured by Busch.

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SELECT 	beer, AVG(price) FROM 	Sells GROUP BY 	beer
HAVING 	COUNT(*) >= 3 OR beer IN (SELECT name FROM Beers
WHERE manf = 'Busch');

如果写成：

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SELECT beer, AVG(price) FROM Sells GROUP BY beer,manf
HAVING COUNT(*) >= 3 OR manf = 'Busch';

如果啤酒和厂商是多对多，count(*)会数少了，数据条数也会变多。

Q1: SELECT DISTINCT a FROM R WHERE b>10;

Q2: SELECT a FROM R WHERE b>10 GROUP BY a;

Q1和Q2产生相同的结果。

R(A,B,C):

Q1: SELECT DISTINCT * FROM R;

Q2: SELECT * FROM R GROUP BY A,B,C;

Q1和Q2产生相同的结果。

More SQL

Modification 增删改

•INSERT INTO relation VALUES (list of values);

•INSERT INTO relation (subquery);

•DELETE FROM relation WHERE condition;

•UPDATE relation SET assignments WHERE condition;

例：

•Create a table of all Sally’s potential buddies, i.e., the people who frequent bars that Sally also frequents.

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CREATE TABLE PotBuddies(name char(30));
INSERT INTO PotBuddies
(SELECT   DISTINCT d2.drinker
FROM    Frequents d1, Frequents d2
WHERE   d1.drinker = 'Sally' AND
d2.drinker <> 'Sally' AND
d1.bar = d2.bar);

基于属性的检查 check

只在插入和更新时起作用，在被参照表删除或更新时，不起作用，区别于外键约束。删除元组时不检查，可能违反约束，区别于assertion。

断言 ASSERTION

总是为真。例：

No bar may charge an avg. of more than $5 for beer.

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CREATE ASSERTION NoRipoffBars
CHECK (NOT EXISTS(
			SELECT bar
			FROM Sells
			GROUP BY bar
			HAVING 5.0 < AVG(price)));

There cannot be more bars than drinkers.

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CREATE ASSERTION FewBar
CHECK( (SELECT COUNT(*) FROM Bars) <=
		        (SELECT COUNT(*) FROM Drinkers));

Trigger

•Whenever a new tuple is inserted into Sells:

–If the beer mentioned is not in Beers, then insert it (with a null manufacturer).

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CREATE TRIGGER BeerTrig
AFTER INSERT ON Sells -- INSERT can be DELETE or UPDATE OF <attr>.
FOR EACH ROW --FOR EACH ROW can be omitted
WHEN(:new.beer NOT IN (SELECT name FROM Beers))
	BEGIN
		INSERT INTO Beers(name) VALUES(:new.beer);
	END;

存储过程

一组为了完成特定功能的Transact-SQL语句集合。

域完整性约束

sql sever的三种机制：缺省值、规则、用户定义的数据类型

局部变量

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DECLARE @avg_budget int,@extra_budget int
	SET @extra_budget=15000
	SELECT @avg_budget=AVG(budget) FROM project
	IF (SELECT budget
	      FROM project
	      WHERE projectno='p1')<@avg_budget
	BEGIN
		UPDATE project
		SET budget=budget+@extra_budget
		WHERE projectno='p1'
		PRINT 'Budget for p1 increased by 15000'
	END
	ELSE 
		PRINT 'Budget for p1 unchanged'

视图

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CREATE VIEW v_count(projectno,countproject)
    AS SELECT projectno,COUNT(*)
          FROM workson
          GROUP BY projectno;

执行CREATE VIEW语句只是把视图的定义存入数据字典，并不执行SELECT语句

SQL Authorization

授权

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GRANT <list of privileges>
		ON <relation or other object>
		TO <list of authorization ID’s>;
		
-- 如果想要接受者可以传递特权，使用：
WITH GRANT OPTION

GRANT SELECT, UPDATE(price) ON Sells TO sally;
-- Sally has the right to issue any query on Sells and can update the price component only
GRANT UPDATE ON Sells TO sally WITH GRANT OPTION;
-- Sally can not only update any attribute of Sells, but can grant to others the privilege UPDATE ON Sells.

收权

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REVOKE <list of privileges>
		ON <relation or other object>
		FROM <list of authorization ID’s>;
--这些用户可能还是可以使用该特权，因为他们可能从其他地方获得授权

两种方式：RESTRICT, CASCADE

授权图

节点

user/privilege/option/isOwner

对于特权，不同属性上的操作是不同的节点，可传递和不可传递特权的用户是不同的节点；节点中AP表示A用户有P特权。P*表示P with grant option。P 表示P的源头，AP 表示A is the owner of the object on which P is a privilege.

边

X->Y，X用来授权Y

•When A grants P to B, we draw an edge from AP * or AP ** to BP.

–Or to BP * if the grant is with grant option.

•If A grants a subprivilege Q of P (say UPDATE(a) on R when P is UPDATE ON R) then the edge goes to BQ or BQ *, instead.

•Fundamental rule: user C has privilege Q as long as there is a path from XQ (the origin of privilege Q ) to CQ, CQ *, or CQ.

–Remember that XQ could be CQ.

•If A revokes P from B with the CASCADE option, delete the edge from AP to BP.

If A uses RESTRICT, and there is an edge from BP to anywhere, then reject the revocation and make no change to the graph.

•Having revised the edges, we must check that each node has a path from some ** node, representing ownership.

•Any node with no such path represents a revoked privilege and is deleted from the diagram.

例题

Initially, user A is the owner of relation R, and no other user holds privileges on R. The following are executed:

by A: GRANT UPDATE ON R TO B

by A: GRANT UPDATE(a) ON R TO C WITH GRANT OPTION

by C: GRANT UPDATE(a) ON R TO B WITH GRANT OPTION

by A: REVOKE UPDATE(a) ON R FROM C CASCADE

Which of the following best describes the status of B’s privileges on R?

(a) B can update any attribute of R except a but cannot grant that privilege.

(b) B has no privileges on R and cannot grant any.

(c) B can update any attribute of R except a, but can grant others the privilege to update R:a .

Consider a database with relation R and users Alice, Bob, Carol, and Dave. Alice owns relation R. The following sequence of operations takes place:

Alice: GRANT SELECT ON R TO Bob WITH GRANT OPTION

Alice: GRANT SELECT ON R TO Carol WITH GRANT OPTION

Carol: GRANT SELECT ON R TO Bob WITH GRANT OPTION

Bob: GRANT SELECT ON R TO Dave WITH GRANT OPTION

Carol: GRANT SELECT ON R TO Dave

Dave: GRANT SELECT ON R TO Carol WITH GRANT OPTION

Alice: REVOKE SELECT ON R FROM Bob CASCADE

After these statements are executed, which of the following statements is true?

(a) Dave has the SELECT ON R privilege, but without the grant option.

(c) Dave does not have the SELECT ON R privilege.

(d) Dave has the grant option for the SELECT ON R privilege, but does not have the privilege itself.

Respect others and your will be respected

写作框架

开头段：开门见山，引出话题

中间段：举例论证重要性、如何做、结果和意义

结尾段：总结、倡导

参考范文

It is a truth universally acknowledged that mutual respect plays a key role in our daily life. Jst as an old saying goes, “Respect others and you will be respected”. Obviously, this proverb teaches us that being respected by others is derived from respecting others.

Why does mutual respect play an important part in our society? Reasons can be listed as follows. First and foremost, all men are created equal which was first written in the U.S. Declaration of Independence. In other words, being respected is the basic right of human being. Moreover, to respect others means understanding others’ situation and respecting others; rights. For me, I have never interrupted others when they are talking or doing their own work. I always keep in mind that without respect, it is hard for me to gain friendship and trust.

In conclusion, respecting others matters a lot in our daily life, which also shows one’s good parenting and quality. The more you respect others, the more you will be respected. Only in this way can we expect our society more harmonious.

title: Words_on_textbook4
tags: CET6—

Unit1

Unit2

Unit3

Unit4

Unit5

再再再复习一遍文件流，不要再忘了好不好……

源代码文件中包含头文件 \ 和 \

打开文件

在从文件读取信息或者向文件写入信息之前，必须先打开文件。open() 成员函数的第一参数指定要打开的文件的名称和位置，第二个参数定义文件被打开的模式。

关闭文件

在程序终止前关闭所有打开的文件，close() 函数。

• 查询字段值是Null的记录

  判断某个值是否为NULL时，应该用is NULL ，而不是is null

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select * from tableA where xxx is null

• 分组统计，数据为空时显示0

（有where条件时，被where条件过滤的数据不显示了）

利用表的关联查询

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select k.catid,count(t.catid) from 
(select catid from Category) k left join 
(select catid from Project left outer join Workson on Project.proid=Workson.proid where empid='10102')t 
on k.catid=t.catid group by k.catid

将 where 换成left outer join… on …. and，用and代替where，在连接的时候过滤，该项会被设为空值，不会在一开始过滤掉需要的空值。另外要注意left outer join 的两张表的顺序

• 查找选修了全部课程的学生学号

等价于找学生学号，对于这个学号，他所选的课程集合为B，不存在课程集合A，使得A不在B中—使用两个not exist 。但是我又想到，也可以去数这个学生选的课程数，这个课程数等于总的课程数。

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select 学号 from student
where not exists 
   (select * from course
    where not exists
        (select * from takes
        where  takes.课号=course.课号
                       and takes.学号=student.学号))

SQL SELECT语句完整的执行顺序：

将bak文件在SQL SERVER中还原时遇到了两个错误：

解决方法： 左上角“选项”，去掉“结尾日志备份”的选项

解决方法： 左上角“选项”，勾选“覆盖现有数据库”

Whether to Attend College at Home or Abroad?

Currently, with studying abroad gains mounting popularity among people, there is a heated debate about whether to attend college at home or abroad. Opinions on this topic vary from person to person. Some see more benefits in studying at home while others claim that studying abroad is a more ideal choice as it’s more challenging.

Personally, I am a strong favorer of the latter view. Listed below are the reasons for my advice. First of all, attending college abroad provides an opportunity to broaden one’s experience and mind. You can acquire cross-cultural experiences and gain new perspectives on your chosen field of study. In addition, studying abroad helps you to polish your social skills; you can make friends with different people with different background. Thirdly, overseas studying is conductive to the formation of an independent, autonomous and tenacious personality, which will ultimately benefit the achievement of our life goals.

Just as an old saying goes: ”It is better to travel thousand miles than to read ten thousand books.” Then studying abroad can not only enable us to reap in our books, but also in our trips. And this is why attending college abroad is a preferable selection for me.

Notes

mounting [ˈmaʊntɪŋ] adj.上升的;增长的

conductive adj. 导电（或热等）的

Singapore is a conductive environment for studies and learningEnglish. 新加坡是个学习英语和搞研究的好环境。

Understanding China’s history and culture is conductive to know Chinese well. 了解中国的历史和文化有助于了解中国人民。

tenacious [təˈneɪʃəs] adj. 顽强的、坚持的

In spite of his illness, he clung（v.抓紧） tenaciously to his job.尽管有病在身，他仍顽强地坚持工作

明朝统治中国276年,被人们描绘成人类理有序、社会稳定的最伟大的时代期,手工业的发展促进了市场经济和城市化。大量商品,包括酒和丝绸,都在市场销售。同时,还进外国商品,如时钟和烟进京、南京/扬州这样的大商继形成。也是在明代郑和率领的船队會到印度洋进大规模探险航行。还值得一提的是,中国文学的四大经典名著中有三部写于明代。

The Ming Dynasty, which ruled China for 276 years, was depicted as one of the greatest eras characterized by good governance and stable society in human history. During this period, the blossom of handicraft industry accelerated the process of market economy and urbanization. A great deal of commodities, wine and silk included, were available on the market. In the meantime, clocks and tobacco products, among many other foreign goods, were imported. Major commercial canters like Beijing, Nanjing, Yangzhou and Suzhou took shape successively. It was also in the Ming Dynasty that fleets headed by navigator Zheng He had made seven large scale expeditions to the Indian Ocean. What’s also noteworthy is that three of the Four Great Classical Novels of Chinese Literature were written in the Ming Dynasty.

Notes

governance [ˈɡʌvərnəns] n. 统治;管理方法

noteworthy [ˈnoʊtwɜːrði] adj. 值得注意的;显著的

the Four Great Classical Novels of Chinese Literature 四大名著

be depicted as … 被描述为…

be characterized/featured by … 具有…特征

the blossom of handicraft industry 手工业的发展

took shape successively 相继形成

最后做性能分析的时候可以记个时。

分支界定法解决背包问题

首先回顾一下0-1背包，dp[i][j]代表前i个物品花费的cost为j，所得到的最大的value。现在有多个背包了，于是再加一个维度，dp[i][j][k]表示前i个物品放到j个背包里，第j个背包花费的cost为k，所得到的最大的value。

我，没有，看懂，那些文献。

能写多少，写多少。

需要剪枝生成一棵树，然后找高度最高的。你觉得，从下向上生成怎么样呢？行不通，最后一个都不一定在里面啊！只能从上向下？

每个节点，有m个孩子，它处在第j层的第i个孩子，表示当前的T[j]用的是第i条彩带，也就等于它自身，做一个修改：第i个位置长度减去T[j]。每次向下延伸一层，都要更新孩子节点，把小于最小需求的位置置为false，全为false时，就是叶节点了。

然后求最大的深度。

今天我们的任务是——拿下算法导论！

最优答案是在里面的，但是这个“33686019”是个什么鬼东西？！出错就出在这了。难道是溢出？？？嗯，加了一个上限，就没问题了，虽然我也不知道他是在哪溢出了。

你肿么二重循环的delete又出问题了？！

Directions

Suppose you are asked to give advice on whether to major in science or humanities at college, write an essay to state your opinion.

Whether to Major in Science or Humanities at College?

Nowadays, as the whole society place increasingly considerable value on education, the question of whether to major in science or humanities at college is not only a concern for students, but also a focal point for parents. Some believe that to dig into science is a better choice because it promises us a brighter future; other may hold the opposite view that humanity knowledge is the foundation of humanity quality.

As for me, both arguments are justified. However, I believe that the important thing is not about which subject is better, what matters most is people who will have to make the decision. In other words, we should not lay one-sided emphasis on the advantages of either subject; on the contrary, the students themselves, their interests and preference, pros and cons are supposed to be taken into consideration. For example, if a student is more adept at humanity where his real interests lie, then he should dedicate to the study on humanity.

Whether to major in science or humanity is a critical choice for every student because its result has a profound influence on personal career development and life style. Thus, we should figure out what we really care about so as not to put the cart before the horse.

notes

1. considerable [kənˈsɪdərəbl] adj. 相当多(或大、重要等)的

   The project wasted a considerable amount of time and money.那项工程耗费了相当多的时间和资金。

2. focal [ˈfoʊkl] adj. 中心的;很重要的;焦点的;

3. dig into 挖掘;调查，刻苦钻研

4. justified [ˈdʒʌstɪfaɪd] adj.(做某事)有正当理由的;事出有因;合乎情理
   v.证明…正确(或正当、有理);对…作出解释;调整使全行排满;使每行排齐

5. pros and cons 利弊

   Motherhood has both its pros and cons. 当妈妈既有好的一面，也有不好的一面。

6. adept [əˈdept] adj. 内行的;熟练的;擅长的 n. 专家，能手

   be adept (at/in sth) | (at/in doing sth) = good at doing sth that is quite difficult

7. put the cart before the horse 本末倒置

   Yet, this is to put the cart before the horse. 不过，这样说是本末倒置。