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Tutorial on principles and applications of database system (047) -- MySQL query (IX): connection query
2022-07-24 00:50:00 【Rsda DBA_ WGX】
Database system principle and Application Tutorial （047）—— MySQL Inquire about （ Nine ）： Link query
Catalog
Join query is to query data from multiple tables , Usually, the data in the two tables connected has a one to many connection , Rely on the foreign key in the child table and the primary key in the corresponding parent table to establish association conditions .
One 、 Syntax format of join query
MySQL The syntax format of connection query is as follows ：
FROM surface 1 [INNER|left outer|right outer] JOIN surface 2
ON surface 1. Foreign keys = surface 2. Primary key
[
[INNER|left outer|right outer] JOIN surface 3
ON surface 2. Foreign keys = surface 3. Primary key
...]
-- or
FROM surface 1, surface 2, surface 3,...
WHERE surface 1. Foreign keys = surface 2. Primary key and surface 2. Foreign keys = surface 3. Primary key ...
/* explain ： （1） Connection type ：[inner] join|（ Internal connection ）,left [outer] join（ Left connection ）,right [outer] join（ The right connection ）. （2） The connection type of the second format is inner connection . */
Two 、 The join of two tables
1、 The cartesian product （CROSS JOIN）
Connect each row in the left table with each row in the right table , The result is all combinations of rows of data in these two tables . Cartesian product is actually a join query without any conditions .
for example ：
mysql> select * from teacher;
+-------+-----------+-----------+-------------+
| t_id | t_name | job_title | phone |
+-------+-----------+-----------+-------------+
| T8001 | Ouyang xiu | professor | 13703735666 |
| T8002 | Hua Luogeng | professor | 13703735888 |
| T8003 | Zhong Nanshan | professor | 13703735675 |
| T8004 | Qian xuesen | professor | 13703735638 |
| T8005 | Li Bai | associate professor | 13703735828 |
| T8006 | Confucius | professor | 13703735457 |
| T8007 | Wang Anshi | associate professor | 13703735369 |
+-------+-----------+-----------+-------------+
7 rows in set (0.00 sec)
mysql> select * from course;
+------+-----------------+-------+
| c_id | c_name | t_id |
+------+-----------------+-------+
| C101 | Ancient literature | T8001 |
| C102 | Advanced mathematics | T8002 |
| C103 | linear algebra | T8002 |
| C104 | Clinical medicine | T8003 |
| C105 | Infectious diseases | T8003 |
| C106 | College Physics | T8004 |
| C107 | Poetry appreciation | T8005 |
| C108 | pedagogy | T8006 |
| C109 | criminal procedure law | T8007 |
| C110 | economic law | T8007 |
+------+-----------------+-------+
10 rows in set (0.00 sec)
mysql> select * from course,teacher;
+------+-----------------+-------+-------+-----------+-----------+-------------+
| c_id | c_name | t_id | t_id | t_name | job_title | phone |
+------+-----------------+-------+-------+-----------+-----------+-------------+
| C101 | Ancient literature | T8001 | T8001 | Ouyang xiu | professor | 13703735666 |
| C101 | Ancient literature | T8001 | T8002 | Hua Luogeng | professor | 13703735888 |
| C101 | Ancient literature | T8001 | T8003 | Zhong Nanshan | professor | 13703735675 |
| C101 | Ancient literature | T8001 | T8004 | Qian xuesen | professor | 13703735638 |
| C101 | Ancient literature | T8001 | T8005 | Li Bai | associate professor | 13703735828 |
| C101 | Ancient literature | T8001 | T8006 | Confucius | professor | 13703735457 |
| C101 | Ancient literature | T8001 | T8007 | Wang Anshi | associate professor | 13703735369 |
| C102 | Advanced mathematics | T8002 | T8001 | Ouyang xiu | professor | 13703735666 |
| C102 | Advanced mathematics | T8002 | T8002 | Hua Luogeng | professor | 13703735888 |
| C102 | Advanced mathematics | T8002 | T8003 | Zhong Nanshan | professor | 13703735675 |
| C102 | Advanced mathematics | T8002 | T8004 | Qian xuesen | professor | 13703735638 |
| C102 | Advanced mathematics | T8002 | T8005 | Li Bai | associate professor | 13703735828 |
| C102 | Advanced mathematics | T8002 | T8006 | Confucius | professor | 13703735457 |
| C102 | Advanced mathematics | T8002 | T8007 | Wang Anshi | associate professor | 13703735369 |
| C103 | linear algebra | T8002 | T8001 | Ouyang xiu | professor | 13703735666 |
| C103 | linear algebra | T8002 | T8002 | Hua Luogeng | professor | 13703735888 |
| C103 | linear algebra | T8002 | T8003 | Zhong Nanshan | professor | 13703735675 |
| C103 | linear algebra | T8002 | T8004 | Qian xuesen | professor | 13703735638 |
| C103 | linear algebra | T8002 | T8005 | Li Bai | associate professor | 13703735828 |
| C103 | linear algebra | T8002 | T8006 | Confucius | professor | 13703735457 |
| C103 | linear algebra | T8002 | T8007 | Wang Anshi | associate professor | 13703735369 |
| C104 | Clinical medicine | T8003 | T8001 | Ouyang xiu | professor | 13703735666 |
| C104 | Clinical medicine | T8003 | T8002 | Hua Luogeng | professor | 13703735888 |
| C104 | Clinical medicine | T8003 | T8003 | Zhong Nanshan | professor | 13703735675 |
| C104 | Clinical medicine | T8003 | T8004 | Qian xuesen | professor | 13703735638 |
| C104 | Clinical medicine | T8003 | T8005 | Li Bai | associate professor | 13703735828 |
| C104 | Clinical medicine | T8003 | T8006 | Confucius | professor | 13703735457 |
| C104 | Clinical medicine | T8003 | T8007 | Wang Anshi | associate professor | 13703735369 |
| C105 | Infectious diseases | T8003 | T8001 | Ouyang xiu | professor | 13703735666 |
| C105 | Infectious diseases | T8003 | T8002 | Hua Luogeng | professor | 13703735888 |
| C105 | Infectious diseases | T8003 | T8003 | Zhong Nanshan | professor | 13703735675 |
| C105 | Infectious diseases | T8003 | T8004 | Qian xuesen | professor | 13703735638 |
| C105 | Infectious diseases | T8003 | T8005 | Li Bai | associate professor | 13703735828 |
| C105 | Infectious diseases | T8003 | T8006 | Confucius | professor | 13703735457 |
| C105 | Infectious diseases | T8003 | T8007 | Wang Anshi | associate professor | 13703735369 |
| C106 | College Physics | T8004 | T8001 | Ouyang xiu | professor | 13703735666 |
| C106 | College Physics | T8004 | T8002 | Hua Luogeng | professor | 13703735888 |
| C106 | College Physics | T8004 | T8003 | Zhong Nanshan | professor | 13703735675 |
| C106 | College Physics | T8004 | T8004 | Qian xuesen | professor | 13703735638 |
| C106 | College Physics | T8004 | T8005 | Li Bai | associate professor | 13703735828 |
| C106 | College Physics | T8004 | T8006 | Confucius | professor | 13703735457 |
| C106 | College Physics | T8004 | T8007 | Wang Anshi | associate professor | 13703735369 |
| C107 | Poetry appreciation | T8005 | T8001 | Ouyang xiu | professor | 13703735666 |
| C107 | Poetry appreciation | T8005 | T8002 | Hua Luogeng | professor | 13703735888 |
| C107 | Poetry appreciation | T8005 | T8003 | Zhong Nanshan | professor | 13703735675 |
| C107 | Poetry appreciation | T8005 | T8004 | Qian xuesen | professor | 13703735638 |
| C107 | Poetry appreciation | T8005 | T8005 | Li Bai | associate professor | 13703735828 |
| C107 | Poetry appreciation | T8005 | T8006 | Confucius | professor | 13703735457 |
| C107 | Poetry appreciation | T8005 | T8007 | Wang Anshi | associate professor | 13703735369 |
| C108 | pedagogy | T8006 | T8001 | Ouyang xiu | professor | 13703735666 |
| C108 | pedagogy | T8006 | T8002 | Hua Luogeng | professor | 13703735888 |
| C108 | pedagogy | T8006 | T8003 | Zhong Nanshan | professor | 13703735675 |
| C108 | pedagogy | T8006 | T8004 | Qian xuesen | professor | 13703735638 |
| C108 | pedagogy | T8006 | T8005 | Li Bai | associate professor | 13703735828 |
| C108 | pedagogy | T8006 | T8006 | Confucius | professor | 13703735457 |
| C108 | pedagogy | T8006 | T8007 | Wang Anshi | associate professor | 13703735369 |
| C109 | criminal procedure law | T8007 | T8001 | Ouyang xiu | professor | 13703735666 |
| C109 | criminal procedure law | T8007 | T8002 | Hua Luogeng | professor | 13703735888 |
| C109 | criminal procedure law | T8007 | T8003 | Zhong Nanshan | professor | 13703735675 |
| C109 | criminal procedure law | T8007 | T8004 | Qian xuesen | professor | 13703735638 |
| C109 | criminal procedure law | T8007 | T8005 | Li Bai | associate professor | 13703735828 |
| C109 | criminal procedure law | T8007 | T8006 | Confucius | professor | 13703735457 |
| C109 | criminal procedure law | T8007 | T8007 | Wang Anshi | associate professor | 13703735369 |
| C110 | economic law | T8007 | T8001 | Ouyang xiu | professor | 13703735666 |
| C110 | economic law | T8007 | T8002 | Hua Luogeng | professor | 13703735888 |
| C110 | economic law | T8007 | T8003 | Zhong Nanshan | professor | 13703735675 |
| C110 | economic law | T8007 | T8004 | Qian xuesen | professor | 13703735638 |
| C110 | economic law | T8007 | T8005 | Li Bai | associate professor | 13703735828 |
| C110 | economic law | T8007 | T8006 | Confucius | professor | 13703735457 |
| C110 | economic law | T8007 | T8007 | Wang Anshi | associate professor | 13703735369 |
+------+-----------------+-------+-------+-----------+-----------+-------------+
70 rows in set (0.01 sec)
2、 Internal connection （INNER JOIN）
The query result contains the public fields of two tables （ The foreign key of the child table and the primary key of the parent table ） Records with equal values . When connecting queries, if the columns that need to be used appear in multiple tables , You need to prefix the column name with the table name to qualify , using 【 Table name . Name 】 In the form of .
There are two forms of inner join query ：
A） Between the tables INNER JOIN or JOIN Express , The connection conditions are in ON Back .
B） The tables are separated by commas , The connection conditions are in WHERE Back .
for example ：
（1） Query the teacher information of each course .
-- Format 1
mysql> select c.*, t_name,job_title,phone from course c,teacher t where c.t_id=t.t_id;
+------+-----------------+-------+-----------+-----------+-------------+
| c_id | c_name | t_id | t_name | job_title | phone |
+------+-----------------+-------+-----------+-----------+-------------+
| C101 | Ancient literature | T8001 | Ouyang xiu | professor | 13703735666 |
| C102 | Advanced mathematics | T8002 | Hua Luogeng | professor | 13703735888 |
| C103 | linear algebra | T8002 | Hua Luogeng | professor | 13703735888 |
| C104 | Clinical medicine | T8003 | Zhong Nanshan | professor | 13703735675 |
| C105 | Infectious diseases | T8003 | Zhong Nanshan | professor | 13703735675 |
| C106 | College Physics | T8004 | Qian xuesen | professor | 13703735638 |
| C107 | Poetry appreciation | T8005 | Li Bai | associate professor | 13703735828 |
| C108 | pedagogy | T8006 | Confucius | professor | 13703735457 |
| C109 | criminal procedure law | T8007 | Wang Anshi | associate professor | 13703735369 |
| C110 | economic law | T8007 | Wang Anshi | associate professor | 13703735369 |
+------+-----------------+-------+-----------+-----------+-------------+
10 rows in set (0.01 sec)
-- Format two
mysql> select c.*, t_name,job_title,phone from course c join teacher t on c.t_id=t.t_id;
+------+-----------------+-------+-----------+-----------+-------------+
| c_id | c_name | t_id | t_name | job_title | phone |
+------+-----------------+-------+-----------+-----------+-------------+
| C101 | Ancient literature | T8001 | Ouyang xiu | professor | 13703735666 |
| C102 | Advanced mathematics | T8002 | Hua Luogeng | professor | 13703735888 |
| C103 | linear algebra | T8002 | Hua Luogeng | professor | 13703735888 |
| C104 | Clinical medicine | T8003 | Zhong Nanshan | professor | 13703735675 |
| C105 | Infectious diseases | T8003 | Zhong Nanshan | professor | 13703735675 |
| C106 | College Physics | T8004 | Qian xuesen | professor | 13703735638 |
| C107 | Poetry appreciation | T8005 | Li Bai | associate professor | 13703735828 |
| C108 | pedagogy | T8006 | Confucius | professor | 13703735457 |
| C109 | criminal procedure law | T8007 | Wang Anshi | associate professor | 13703735369 |
| C110 | economic law | T8007 | Wang Anshi | associate professor | 13703735369 |
+------+-----------------+-------+-----------+-----------+-------------+
10 rows in set (0.00 sec)
3、 External connection
The outer connection includes the left connection （LEFT OUTER JOIN）、 The right connection （RIGHT OUTER JOIN）、 Complete connection （FULL OUTER JOIN,MySQL I won't support it ）. The meanings of various external connections are as follows ：
A） Left connection ： The result set includes rows that meet the specified connection conditions after two tables are connected , It also shows JOIN All rows in the table on the left of the keyword that meet the search conditions , How can a row in the left table have no matching row in the right table , Then in the result , All the selected columns in the right table are NULL.
B） The right connection ： Is the reverse connection of the left connection .
C） Complete connection ： The result set of a complete outer join query includes the result set of two inner join tables and rows that do not meet the conditions in the left table and the right table .
（1） stay course and teacher Insert the following data into the table ：
mysql> insert into course values('C111', ' College English I',NULL);
Query OK, 1 row affected (0.00 sec)
mysql> insert into course values('C112', ' College English II',NULL);
Query OK, 1 row affected (0.00 sec)
mysql> select * from course;
+------+-----------------+-------+
| c_id | c_name | t_id |
+------+-----------------+-------+
| C101 | Ancient literature | T8001 |
| C102 | Advanced mathematics | T8002 |
| C103 | linear algebra | T8002 |
| C104 | Clinical medicine | T8003 |
| C105 | Infectious diseases | T8003 |
| C106 | College Physics | T8004 |
| C107 | Poetry appreciation | T8005 |
| C108 | pedagogy | T8006 |
| C109 | criminal procedure law | T8007 |
| C110 | economic law | T8007 |
| C111 | College English I | NULL |
| C112 | College English II | NULL |
+------+-----------------+-------+
12 rows in set (0.00 sec)
mysql> insert into teacher values('T8008',' Qian Zhongshu ',' professor ','13637351245');
Query OK, 1 row affected (0.00 sec)
mysql> insert into teacher values('T8009',' Lin Huiyin ',' professor ','13637354548');
Query OK, 1 row affected (0.00 sec)
mysql> select * from teacher;
+-------+-----------+-----------+-------------+
| t_id | t_name | job_title | phone |
+-------+-----------+-----------+-------------+
| T8001 | Ouyang xiu | professor | 13703735666 |
| T8002 | Hua Luogeng | professor | 13703735888 |
| T8003 | Zhong Nanshan | professor | 13703735675 |
| T8004 | Qian xuesen | professor | 13703735638 |
| T8005 | Li Bai | associate professor | 13703735828 |
| T8006 | Confucius | professor | 13703735457 |
| T8007 | Wang Anshi | associate professor | 13703735369 |
| T8008 | Qian Zhongshu | professor | 13637351245 |
| T8009 | Lin Huiyin | professor | 13637354548 |
+-------+-----------+-----------+-------------+
9 rows in set (0.00 sec)
（2） Query the teacher information of all courses .
-- Using the left link, you can query the courses that have no teachers for the time being , here , The corresponding teacher information of this course is NULL value
mysql> select c.*, t_name,job_title,phone
-> from course c left join teacher t on c.t_id=t.t_id;
+------+-----------------+-------+-----------+-----------+-------------+
| c_id | c_name | t_id | t_name | job_title | phone |
+------+-----------------+-------+-----------+-----------+-------------+
| C101 | Ancient literature | T8001 | Ouyang xiu | professor | 13703735666 |
| C102 | Advanced mathematics | T8002 | Hua Luogeng | professor | 13703735888 |
| C103 | linear algebra | T8002 | Hua Luogeng | professor | 13703735888 |
| C104 | Clinical medicine | T8003 | Zhong Nanshan | professor | 13703735675 |
| C105 | Infectious diseases | T8003 | Zhong Nanshan | professor | 13703735675 |
| C106 | College Physics | T8004 | Qian xuesen | professor | 13703735638 |
| C107 | Poetry appreciation | T8005 | Li Bai | associate professor | 13703735828 |
| C108 | pedagogy | T8006 | Confucius | professor | 13703735457 |
| C109 | criminal procedure law | T8007 | Wang Anshi | associate professor | 13703735369 |
| C110 | economic law | T8007 | Wang Anshi | associate professor | 13703735369 |
| C111 | College English I | NULL | NULL | NULL | NULL |
| C112 | College English II | NULL | NULL | NULL | NULL |
+------+-----------------+-------+-----------+-----------+-------------+
12 rows in set (0.00 sec)
（3） Query the course information undertaken by all teachers .
-- Using the right connection, you can query the information of teachers who do not undertake any courses , here , The corresponding course information of the teacher is NULL value
mysql> select c.*, t_name,job_title,phone
-> from course c right join teacher t on c.t_id=t.t_id;
+------+-----------------+-------+-----------+-----------+-------------+
| c_id | c_name | t_id | t_name | job_title | phone |
+------+-----------------+-------+-----------+-----------+-------------+
| C101 | Ancient literature | T8001 | Ouyang xiu | professor | 13703735666 |
| C102 | Advanced mathematics | T8002 | Hua Luogeng | professor | 13703735888 |
| C103 | linear algebra | T8002 | Hua Luogeng | professor | 13703735888 |
| C104 | Clinical medicine | T8003 | Zhong Nanshan | professor | 13703735675 |
| C105 | Infectious diseases | T8003 | Zhong Nanshan | professor | 13703735675 |
| C106 | College Physics | T8004 | Qian xuesen | professor | 13703735638 |
| C107 | Poetry appreciation | T8005 | Li Bai | associate professor | 13703735828 |
| C108 | pedagogy | T8006 | Confucius | professor | 13703735457 |
| C109 | criminal procedure law | T8007 | Wang Anshi | associate professor | 13703735369 |
| C110 | economic law | T8007 | Wang Anshi | associate professor | 13703735369 |
| NULL | NULL | NULL | Qian Zhongshu | professor | 13637351245 |
| NULL | NULL | NULL | Lin Huiyin | professor | 13637354548 |
+------+-----------------+-------+-----------+-----------+-------------+
12 rows in set (0.00 sec)
（4） Query the teacher information of all courses and the course information of all teachers . because MySQL Full connection is not supported , have access to UNION Merge the left join and the right join to get the query result .
/* select c.*, t_name,job_title,phone from course c left join teacher t on c.t_id=t.t_id union select c.*, t_name,job_title,phone from course c right join teacher t on c.t_id=t.t_id; */
mysql> select c.*, t_name,job_title,phone
-> from course c left join teacher t on c.t_id=t.t_id
-> union
-> select c.*, t_name,job_title,phone
-> from course c right join teacher t on c.t_id=t.t_id;
+------+-----------------+-------+-----------+-----------+-------------+
| c_id | c_name | t_id | t_name | job_title | phone |
+------+-----------------+-------+-----------+-----------+-------------+
| C101 | Ancient literature | T8001 | Ouyang xiu | professor | 13703735666 |
| C102 | Advanced mathematics | T8002 | Hua Luogeng | professor | 13703735888 |
| C103 | linear algebra | T8002 | Hua Luogeng | professor | 13703735888 |
| C104 | Clinical medicine | T8003 | Zhong Nanshan | professor | 13703735675 |
| C105 | Infectious diseases | T8003 | Zhong Nanshan | professor | 13703735675 |
| C106 | College Physics | T8004 | Qian xuesen | professor | 13703735638 |
| C107 | Poetry appreciation | T8005 | Li Bai | associate professor | 13703735828 |
| C108 | pedagogy | T8006 | Confucius | professor | 13703735457 |
| C109 | criminal procedure law | T8007 | Wang Anshi | associate professor | 13703735369 |
| C110 | economic law | T8007 | Wang Anshi | associate professor | 13703735369 |
| C111 | College English I | NULL | NULL | NULL | NULL |
| C112 | College English II | NULL | NULL | NULL | NULL |
| NULL | NULL | NULL | Qian Zhongshu | professor | 13637351245 |
| NULL | NULL | NULL | Lin Huiyin | professor | 13637354548 |
+------+-----------------+-------+-----------+-----------+-------------+
14 rows in set (0.02 sec)
3、 ... and 、 Multiple table joins
The connection query of multiple tables can be understood in this way ： First, join the two tables to generate a new table , Then use this new table to join and query with the third table , And so on .
The syntax is as follows ：
FROM surface 1 [INNER] JOIN surface 2 ON surface 1. Foreign keys = surface 2. Primary key
[
[INNER] JOIN surface 3 ON surface 2. Foreign keys = surface 3. Primary key
...]
-- or
FROM surface 1, surface 2, surface 3,...
WHERE surface 1. Foreign keys = surface 2. Primary key and surface 2. Foreign keys = surface 3. Primary key ...
for example ：
（1） Query students' course selection information , Including the student number of the student , full name , The course number of the course , Course name and grades .
/* select s.s_id, s.s_name, c.c_id, c.c_name, score from student s join score sc on s.s_id = sc.s_id join course c on c.c_id = sc.c_id; */
mysql> select s.s_id, s.s_name, c.c_id, c.c_name, score
-> from student s join score sc on s.s_id = sc.s_id
-> join course c on c.c_id = sc.c_id;
+-------+-----------+------+-----------------+-------+
| s_id | s_name | c_id | c_name | score |
+-------+-----------+------+-----------------+-------+
| S2011 | Zhang Xiaogang | C102 | Advanced mathematics | 84 |
| S2011 | Zhang Xiaogang | C105 | Infectious diseases | 90 |
| S2011 | Zhang Xiaogang | C106 | College Physics | 79 |
| S2011 | Zhang Xiaogang | C109 | criminal procedure law | 65 |
| S2012 | Liu Xiaoqing | C101 | Ancient literature | 67 |
| S2012 | Liu Xiaoqing | C102 | Advanced mathematics | 52 |
| S2012 | Liu Xiaoqing | C103 | linear algebra | 55 |
| S2012 | Liu Xiaoqing | C104 | Clinical medicine | 86 |
| S2012 | Liu Xiaoqing | C105 | Infectious diseases | 87 |
| S2012 | Liu Xiaoqing | C106 | College Physics | 64 |
| S2012 | Liu Xiaoqing | C107 | Poetry appreciation | 62 |
| S2012 | Liu Xiaoqing | C108 | pedagogy | 73 |
| S2012 | Liu Xiaoqing | C109 | criminal procedure law | 78 |
| S2012 | Liu Xiaoqing | C110 | economic law | 89 |
| S2013 | Cao mengde | C102 | Advanced mathematics | 97 |
| S2013 | Cao mengde | C103 | linear algebra | 68 |
| S2013 | Cao mengde | C104 | Clinical medicine | 66 |
| S2013 | Cao mengde | C105 | Infectious diseases | 68 |
| S2014 | Liu Yan | C102 | Advanced mathematics | 90 |
| S2014 | Liu Yan | C103 | linear algebra | 85 |
| S2014 | Liu Yan | C104 | Clinical medicine | 77 |
| S2014 | Liu Yan | C105 | Infectious diseases | 96 |
| S2015 | Liu Yan | C101 | Ancient literature | 69 |
| S2015 | Liu Yan | C102 | Advanced mathematics | 66 |
| S2015 | Liu Yan | C103 | linear algebra | 88 |
| S2015 | Liu Yan | C104 | Clinical medicine | 69 |
| S2015 | Liu Yan | C105 | Infectious diseases | 66 |
| S2015 | Liu Yan | C106 | College Physics | 88 |
| S2015 | Liu Yan | C107 | Poetry appreciation | 69 |
| S2015 | Liu Yan | C108 | pedagogy | 66 |
| S2015 | Liu Yan | C109 | criminal procedure law | 88 |
| S2015 | Liu Yan | C110 | economic law | 69 |
| S2016 | Liu Ruofei | C101 | Ancient literature | 65 |
| S2016 | Liu Ruofei | C102 | Advanced mathematics | 69 |
| S2016 | Liu Ruofei | C107 | Poetry appreciation | 82 |
| S2016 | Liu Ruofei | C108 | pedagogy | 56 |
| S2021 | Dong Wenhua | C102 | Advanced mathematics | 72 |
| S2021 | Dong Wenhua | C103 | linear algebra | 90 |
| S2021 | Dong Wenhua | C104 | Clinical medicine | 90 |
| S2021 | Dong Wenhua | C105 | Infectious diseases | 57 |
| S2022 | Zhou Huajian | C102 | Advanced mathematics | 88 |
| S2022 | Zhou Huajian | C103 | linear algebra | 93 |
| S2022 | Zhou Huajian | C109 | criminal procedure law | 47 |
| S2022 | Zhou Huajian | C110 | economic law | 62 |
| S2023 | trump | C102 | Advanced mathematics | 68 |
| S2023 | trump | C103 | linear algebra | 86 |
| S2023 | trump | C109 | criminal procedure law | 56 |
| S2023 | trump | C110 | economic law | 91 |
| S2024 | Obama | C102 | Advanced mathematics | 87 |
| S2024 | Obama | C103 | linear algebra | 97 |
| S2024 | Obama | C109 | criminal procedure law | 80 |
| S2024 | Obama | C110 | economic law | 81 |
| S2025 | Zhou Jianhua | C102 | Advanced mathematics | 61 |
| S2025 | Zhou Jianhua | C105 | Infectious diseases | 62 |
| S2025 | Zhou Jianhua | C106 | College Physics | 87 |
| S2025 | Zhou Jianhua | C109 | criminal procedure law | 82 |
| S2026 | Zhang Xueyou | C102 | Advanced mathematics | 59 |
| S2026 | Zhang Xueyou | C105 | Infectious diseases | 48 |
| S2026 | Zhang Xueyou | C106 | College Physics | 90 |
| S2026 | Zhang Xueyou | C109 | criminal procedure law | 73 |
+-------+-----------+------+-----------------+-------+
60 rows in set (0.00 sec)
（2） Inquire about 【 trump 】 Classmate 【 Advanced mathematics 】 achievement
/* select score from student s, course c, score sc where s.s_id = sc.s_id and c.c_id = sc.c_id and s_name = ' trump ' and c_name = ' Advanced mathematics '; */
mysql> select score
-> from student s, course c, score sc
-> where s.s_id = sc.s_id and c.c_id = sc.c_id
-> and s_name = ' trump ' and c_name = ' Advanced mathematics ';
+-------+
| score |
+-------+
| 68 |
+-------+
1 row in set (0.00 sec)
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