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/* Author: Chenhui Wang
   Date: 2018-05-27  */

-- 一种设置唯一性表格的方法
create table person(
	first_name char(20) not null,
	last_name char(20) not null,
	sex char(10),
	primary key (last_name, first_name) -- First approach
)

-- 这样如果插入两个相同的数据，就会报错

create table person(
	first_name char(20) not null,
	last_name char(20) not null,
	sex char(10),
	UNIQUE (last_name, first_name) -- Second approach
)
-- 相同的效果
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-- 如果想统计重复的数据，用系统内置函数count(*)
/*
person table
+------------+-----------+--------+
| first_name | last_name | sex    |
+------------+-----------+--------+
| Chenhui    | Wang      | Male   |
| Chenhui    | Wang      | Male   |
| Chenhui    | Wang      | Male   |
| Huiqian    | Ying      | Female |
| Huiqian    | Ying      | Female |
| Jiahuan    | He        | Female |
| Luting     | Sun       | Female |
+------------+-----------+--------+
*/
select count(*) as repetitions, first_name, last_name from person group by last_name, first_name having repetitions > 1;
/*
+-------------+-----------+------------+
| repetitions | last_name | first_name |
+-------------+-----------+------------+
|           3 | Wang      | Chenhui    |
|           2 | Ying      | Huiqian    |
+-------------+-----------+------------+
*/
select first_name, count(*) from person group by first_name;
/*
+------------+----------+
| first_name | count(*) |
+------------+----------+
| Chenhui    |        3 |
| Huiqian    |        2 |
| Jiahuan    |        1 |
| Luting     |        1 |
+------------+----------+
*/
-- 去除重复元素，比如person列表中重复的
create table tmp select first_name, last_name, sex from person group by first_name, last_name, sex;
drop table person;
alter table tmp rename to person;
-- 或者
create table person_clone select distinct first_name, last_name, sex from person; --感觉这种最好
/*
+------------+-----------+--------+
| first_name | last_name | sex    |
+------------+-----------+--------+
| Chenhui    | Wang      | Male   |
| Huiqian    | Ying      | Female |
| Jiahuan    | He        | Female |
| Luting     | Sun       | Female |
+------------+-----------+--------+
*/

-- 导出table
select * from person into outfile 'C:/Users/Link/Desktop/ass.txt' -- 格式很乱
select * from person into outfile 'C:/Users/Link/Desktop/ass.txt' fields terminated by ',', enclosed by '"' lines terminated by '\r\n';
/*
结果会生成一个txt文件，内容如下
"Chenhui","Wang","Male"
"Chenhui","Wang","Male"
"Chenhui","Wang","Male"
"Huiqian","Ying","Female"
"Huiqian","Ying","Female"
"Jiahuan","He","Female"
"Luting","Sun","Female"
*/
-- 在多个表进行操作时，如果操作的是两个表共有的属性，要加.表示身份
/*
instructor
+-------+------------+-----------+----------+
| ID    | name       | dept_name | salary   |
+-------+------------+-----------+----------+
| 10101 | Srinivasan | Comp.Sci. | 65000.00 |
| 12121 | Wu         | Finance   | 90000.00 |
| 15151 | Mozart     | Music     | 40000.00 |
| 22222 | Einstein   | Physics   | 95000.00 |
| 32343 | El Said    | History   | 60000.00 |
| 33456 | Gold       | Physics   | 87000.00 |
| 45565 | Katz       | Comp.Sci. | 75000.00 |
| 58583 | Califieri  | History   | 62000.00 |
| 76543 | Singh      | Finance   | 80000.00 |
| 83821 | Brandt     | Comp.Sci. | 92000.00 |
| 98345 | Kim        | Elec.Eng. | 80000.00 |
+-------+------------+-----------+----------+

department
+-----------+----------+-----------+
| dept_name | building | budget    |
+-----------+----------+-----------+
| Biology   | Watson   |  90000.00 |
| Comp.Sci. | Taylor   | 100000.00 |
| Elec.Eng. | Taylor   |  85000.00 |
| Finance   | Painter  | 120000.00 |
| History   | Painter  |  50000.00 |
| Music     | Packard  |  80000.00 |
| Physics   | Watson   |  70000.00 |
+-----------+----------+-----------+

teaches
+-------+-----------+--------+----------+------+
| ID    | course_id | sec_id | semester | year |
+-------+-----------+--------+----------+------+
| 10101 | CS-101    | 1      | Fall     | 2009 |
| 45565 | CS-101    | 1      | Spring   | 2010 |
| 83821 | CS-190    | 1      | Spring   | 2009 |
| 83821 | CS-190    | 2      | Spring   | 2009 |
| 10101 | CS-315    | 1      | Spring   | 2010 |
| 45565 | CS-319    | 1      | Spring   | 2010 |
| 10101 | CS-347    | 1      | Fall     | 2009 |
| 10101 | EE-181    | 1      | Spring   | 2009 |
| 98345 | EE-181    | 1      | Spring   | 2009 |
| 12121 | FIN-201   | 1      | Spring   | 2010 |
| 32343 | HIS-351   | 1      | Spring   | 2010 |
| 15151 | MU-119    | 1      | Spring   | 2010 |
| 22222 | PHY-001   | 1      | Fall     | 2009 |
+-------+-----------+--------+----------+------+
course 
+-----------+---------------------------+-----------+---------+
| course_id | title                     | dept_name | credits |
+-----------+---------------------------+-----------+---------+
| BIO-101   | Intro.to Biology          | Biology   |       4 |
| BIO-301   | Genetics                  | Biology   |       4 |
| BIO-399   | Computational Biology     | Biology   |       3 |
| CS-101    | Intro.to Computer Science | Comp.Sci. |       4 |
| CS-190    | Game Design               | Comp.Sci. |       4 |
| CS-315    | Robotics                  | Comp.Sci. |       3 |
| CS-319    | Image Processing          | Comp.Sci. |       3 |
| CS-347    | Database System Concepts  | Comp.Sci. |       3 |
| EE-181    | Intro.to Digital Systems  | Elec.Eng. |       3 |
| FIN-201   | Investment Banking        | Finance   |       3 |
| HIS-351   | World History             | History   |       3 |
| MU-119    | Music Video Production    | Music     |       3 |
| PHY-001   | Physical Principles       | Physics   |       4 |
+-----------+---------------------------+-----------+---------+
*/
select name, instructor.dept_name, building from instructor, department where instructor.dept_name = department.dept_name
/*

result
+------------+-----------+----------+
| name       | dept_name | building |
+------------+-----------+----------+
| Srinivasan | Comp.Sci. | Taylor   |
| Katz       | Comp.Sci. | Taylor   |
| Brandt     | Comp.Sci. | Taylor   |
| Kim        | Elec.Eng. | Taylor   |
| Wu         | Finance   | Painter  |
| Singh      | Finance   | Painter  |
| El Said    | History   | Painter  |
| Califieri  | History   | Painter  |
| Mozart     | Music     | Packard  |
| Einstein   | Physics   | Watson   |
| Gold       | Physics   | Watson   |
+------------+-----------+----------+

*/
-- Natural join 自然连接
-- 对所有教师，找出他们的姓名以及所讲的课的代码
select name, course_id from instructor, teaches where instructor.ID = teaches.ID;
/*
result
+------------+-----------+
| name       | course_id |
+------------+-----------+
| Srinivasan | CS-101    |
| Srinivasan | CS-315    |
| Srinivasan | CS-347    |
| Srinivasan | EE-181    |
| Wu         | FIN-201   |
| Mozart     | MU-119    |
| Einstein   | PHY-001   |
| El Said    | HIS-351   |
| Katz       | CS-101    |
| Katz       | CS-319    |
| Brandt     | CS-190    |
| Brandt     | CS-190    |
| Kim        | EE-181    |
+------------+-----------+
*/
-- 或者用natural join，其本质是用第一个关系的每个元组去与第二个关系的元组进行连接，但是元组要在公共属性上取值一样才会被连接。
select name, course_id from instructor natural join teaches; -- 结果和上面一样
-- 下面展示一般的笛卡尔积和natural join有什么不同
select * from instructor join teaches; -- 普通的笛卡尔积，即用第一个关系的每个元组去与第二个关系的元组进行连接，会有mxn个结果，m，n分别是第一，二个元组个数
select * from instructor natural join teaches;
/*
result
+-------+------------+-----------+----------+-----------+--------+----------+------+
| ID    | name       | dept_name | salary   | course_id | sec_id | semester | year |
+-------+------------+-----------+----------+-----------+--------+----------+------+
| 10101 | Srinivasan | Comp.Sci. | 65000.00 | CS-101    | 1      | Fall     | 2009 |
| 10101 | Srinivasan | Comp.Sci. | 65000.00 | CS-315    | 1      | Spring   | 2010 |
| 10101 | Srinivasan | Comp.Sci. | 65000.00 | CS-347    | 1      | Fall     | 2009 |
| 10101 | Srinivasan | Comp.Sci. | 65000.00 | EE-181    | 1      | Spring   | 2009 |
| 12121 | Wu         | Finance   | 90000.00 | FIN-201   | 1      | Spring   | 2010 |
| 15151 | Mozart     | Music     | 40000.00 | MU-119    | 1      | Spring   | 2010 |
| 22222 | Einstein   | Physics   | 95000.00 | PHY-001   | 1      | Fall     | 2009 |
| 32343 | El Said    | History   | 60000.00 | HIS-351   | 1      | Spring   | 2010 |
| 45565 | Katz       | Comp.Sci. | 75000.00 | CS-101    | 1      | Spring   | 2010 |
| 45565 | Katz       | Comp.Sci. | 75000.00 | CS-319    | 1      | Spring   | 2010 |
| 83821 | Brandt     | Comp.Sci. | 92000.00 | CS-190    | 1      | Spring   | 2009 |
| 83821 | Brandt     | Comp.Sci. | 92000.00 | CS-190    | 2      | Spring   | 2009 |
| 98345 | Kim        | Elec.Eng. | 80000.00 | EE-181    | 1      | Spring   | 2009 |
+-------+------------+-----------+----------+-----------+--------+----------+------+
*/
-- instructor 与 teaches公共属性为id，所以只进行id属性上的笛卡尔积

-- 列出教师名字和所教授课程的名字
select name, title from instructor, course where instructor.dept_name = course.dept_name; --这种方法不行，因为没有哪个教师教哪门课的信息
select name, title from instructor natural join teaches, course where teaches.course_id = course.course_id; -- instructor先与teaches做自然连接，再与course匹配。