SQL addition, deletion, modification and query (for example, students, courses, and course selection tables)

Initial table structure and content

Contains three tables of Student, Course and SC (student information table, course information table and course selection result table respectively)

1.1 Student table structure

1.2 Course table structure

1.3 SC table structure

2.1 Student content

2.2 Course content

SELECT * FROM Course ORDER BY cast(Cno as int);

2.3 SC content

Insert data

INSERT INTO Student VALUES('201212126','WANGHUA','MALE',18,'CS');

delete data

DELETE FROM Course WHERE Cno = '11';

update data

UPDATE Course SET Cno = '8' WHERE Cno = '11';

Find data

1. Single table query

SELECT Sno, Sname FROM Student;

SELECT Sname, 2021-Sage FROM Student;

SELECT Sname NAME,
'Year of Birth:' BIRTH, 
2021-Sage BIRTHDAY,
LOWER(Sdept) DEPARTMENT 
FROM Student;

SELECT Sno FROM SC;

SELECT DISTINCT Sno FROM SC;

SELECT Sname FROM Student WHERE Sdept = 'CS';

SELECT Sname, Sage FROM Student WHERE Sage<20;

SELECT Sname, Sdept, Sage FROM Student WHERE Sage (NOT) BETWEEN 19 AND 20;

SELECT Sname, Sdept, Sage FROM Student WHERE Sage BETWEEN 19 AND 20;

(NOT)

SELECT Sname, Ssex FROM Student WHERE Sdept IN('CS','IS');

Fuzzy query
wildcard: _%

SELECT * FROM Student WHERE Sno LIKE '201212121';

SELECT * FROM Course WHERE Cno = '2';

SELECT * FROM Course WHERE Cno LIKE '2';

SELECT * FROM Course WHERE Cno LIKE '2%';

SELECT Sname FROM Student WHERE Sname LIKE 'LIU%';

SELECT Sname FROM Student WHERE Sname LIKE '___CHEN%';

INSERT INTO Course VALUES('9','DBADESIGN','',4);

SELECT * FROM Course WHERE Cname LIKE 'DB_DESIGN%';

SELECT * FROM Course WHERE Cname LIKE 'DB\_DESIGN%' ESCAPE'\';

Aggregate function

Total number of students

SELECT COUNT(*) FROM Student;

Average grade for elective 1

SELECT AVG(Grade) FROM SC WHERE Cno = '1';

Student's total credits for 201212121 elective courses

SELECT SUM(Ccredit) FROM SC,Course 
WHERE Sno = '201212121' AND SC.Cno = Course.Cno;

GROUP BY

Each course number and corresponding number of courses

SELECT Cno, COUNT(Sno) FROM SC GROUP BY Cno;

Link query

The situation of each student and their elective courses

SELECT Student.*, SC.* FROM Student,SC WHERE  Student.Sno = SC.Sno;

Natural connection

SELECT Student.Sno, Sname, Ssex, Sage, Sdept, Cno, Grade
FROM Student, SC WHERE Student.Sno = SC.Sno;

Student ID and name of students who take No. 2 course and have scores below 90 points

SELECT Student.Sno, Sname FROM Student, SC 
WHERE Student.Sno = SC.Sno AND SC.Cno = '2' AND SC.Grade<=90;

Self-connection

Query the prerequisites of each course (comparison)

 SELECT FIRST.Cno,SECOND.Cpno FROM Course FIRST, Course SECOND 
 WHERE FIRST.Cpno = SECOND.Cno;

SELECT Cno,Cpno FROM Course WHERE Cpno = Cno;

SELECT FIRST.Cno,FIRST.Cpno FROM Course FIRST,Course 
WHERE FIRST.Cpno = FIRST.Cno;

Outer join

SELECT Student.Sno, Sname, Sname, Ssex, Sage, Sdept,Cno,Grade 
FROM Student LEFT OUTER JOIN SC ON (Student.Sno = SC.Sno); 

Multi-table join

Query each student's student ID, name, elective courses and grades

SELECT Student.Sno, Sname, Cname, Grade FROM Student,SC,Course
 WHERE Student.Sno = SC.Sno AND SC.Cno = Course.Cno;

Nested query

The name of the student who selected course 2

SELECT Sname FROM Student WHERE Sno IN 
(SELECT Sno FROM SC WHERE Cno = '2');

The number of the course for each student that exceeds the average grade of his own elective course

SELECT Sno, Cno FROM SC x 
WHERE Grade >=(SELECT AVG(Grade) FROM SC y WHERE y.Sno = x.Sno);

Collection query

Computer science students and students younger than 19 years old

SELECT * FROM Student WHERE Sdept = 'CS' 
UNION SELECT * FROM Student WHERE Sage<=19;

The intersection of computer science students and age 19 or younger

SELECT * FROM Student WHERE Sdept = 'CS' 
INTERSECT SELECT * FROM Student WHERE Sage<=19;

The difference between a student in the Department of Computer Science and Technology and a student younger than 19 years old

SELECT * FROM Student WHERE Sdept = 'CS' 
EXCEPT SELECT * FROM Student WHERE Sage<=19;

Query based on derived table

Find out the course number of each student that exceeds his own elective course average

SELECT Sno, Cno 
FROM SC, (SELECT Sno, Avg(Grade) FROM SC GROUP BY Sno) 
AS Avg_sc(avg_sno,avg_grade)
WHERE SC.Sno = Avg_sc.avg_sno AND SC.Grade >= Avg_sc.avg_grade;