成为（SQL大师）的秘诀——极少人知道的秘诀

た入场券 2024-02-18 12:50 33阅读 0赞

## 一.前期准备 ##

### 建表语句 ###

#### 学⽣表 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');

#### 课程表 Course ####

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');

#### 教师表 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');

#### 成绩表 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);

## 二.50道封神题 ##

### 1.查询" 01 “课程比” 02 "课程成绩高的学生的信息及课程分数 ###

> 分析：  
> 1、找出有01成绩的学生成绩信息  
> 2、找出有02成绩的学生成绩信息  
> 3、通过SId将两表取别名t1、t2进行左连接  
> 4、加上满足01‘语文’ > 02’数学’的条件

### 2.查询不存在" 01 “课程但存在” 02 "课程的情况 ###

### 查询平均成绩⼤于等于 60 分的同学的学生编号和学生姓名和平均成绩 ###