The secret to becoming a (SQL Master) – a secret that few people know

1. Preliminary preparation

Create table statement

Student table Student

create table Student(
    SId varchar(10),
    Sname varchar(10),
    Sage datetime,
    Ssex varchar(10)
); 

#-- 学生表 Student
#-- 学生表 Student
insert into Student values('01' , '赵雷' , '1990-01-01' , '男'); 
insert into Student values('02' , '钱电' , '1990-12-21' , '男'); 
insert into Student values('03' , '孙风' , '1990-12-20' , '男'); 
insert into Student values('04' , '李云' , '1990-12-06' , '男'); 
insert into Student values('05' , '周梅' , '1991-12-01' , '女'); 
insert into Student values('06' , '吴兰' , '1992-01-01' , '女'); 
insert into Student values('07' , '郑竹' , '1989-01-01' , '女'); 
insert into Student values('09' , '张三' , '2017-12-20' , '女'); 
insert into Student values('10' , '李四' , '2017-12-25' , '女'); 
insert into Student values('11' , '李四' , '2012-06-06' , '女'); 
insert into Student values('12' , '赵六' , '2013-06-13' , '女'); 
insert into Student values('13' , '孙七' , '2014-06-01' , '女'); 

Course Schedule

create table Course(
    CId varchar(10),
    Cname nvarchar(10),
    TId varchar(10)
);
# -- 科⽬表 Course 
insert into Course values('01' , '语文' , '02'); 
insert into Course values('02' , '数学' , '01'); 
insert into Course values('03' , '英语' , '03');

Teacher list Teacher

create table Teacher(
    TId varchar(10),
    Tname varchar(10)
);
# -- 教师表 Teacher 
insert into Teacher values('01' , '张三'); 
insert into Teacher values('02' , '李四'); 
insert into Teacher values('03' , '王五'); 

Score Sheet SC

create table SC(
    SId varchar(10),
    CId varchar(10),
    score decimal(18,1)
);
# -- 成绩表 SC 
insert into SC values('01' , '01' , 80); 
insert into SC values('01' , '02' , 90); 
insert into SC values('01' , '03' , 99); 
insert into SC values('02' , '01' , 70); 
insert into SC values('02' , '02' , 60); 
insert into SC values('02' , '03' , 80); 
insert into SC values('03' , '01' , 80); 
insert into SC values('03' , '02' , 80); 
insert into SC values('03' , '03' , 80); 
insert into SC values('04' , '01' , 50); 
insert into SC values('04' , '02' , 30); 
insert into SC values('04' , '03' , 20); 
insert into SC values('05' , '01' , 76); 
insert into SC values('05' , '02' , 87); 
insert into SC values('06' , '01' , 31); 
insert into SC values('06' , '03' , 34); 
insert into SC values('07' , '02' , 89); 
insert into SC values('07' , '03' , 98);

2.50 Questions on Conferring Gods

1. Query" 01 "Course Ratio" 02 "information and course scores of students with high course scores

Analysis:
1. Find the score information of students with 01 score
2. Find the score information of students with 02 score 4. Add the conditions that satisfy 01'Chinese' > 02'Mathematics'
3. Use SId to alias the two tables t1 and t2 for left join

2. Query the situation of "01 "course but exists" 02 "course does not exist"

Query the student number, student name and average score of students whose average score is greater than or equal to 60 points