SQL數(shù)據(jù)庫(kù)十四種案例介紹

更新時(shí)間：2021年12月24日 10:19:32 作者：C君莫笑

大家好，本篇文章主要講的是SQL數(shù)據(jù)庫(kù)十四種案例介紹，感興趣的同學(xué)趕快來(lái)看一看吧，對(duì)你有幫助的話記得收藏一下，方便下次瀏覽

數(shù)據(jù)表

/*
Navicat SQLite Data Transfer

Source Server         : school
Source Server Version : 30808
Source Host           : :0

Target Server Type    : SQLite
Target Server Version : 30808
File Encoding         : 65001

Date: 2021-12-23 16:06:04
*/

PRAGMA foreign_keys = OFF;

-- ----------------------------
-- Table structure for Course
-- ----------------------------
DROP TABLE IF EXISTS "main"."Course";
CREATE TABLE Course(
    courseid integer  primary key autoincrement,
    courseme varchar(32),
    teacherid int
);

-- ----------------------------
-- Records of Course
-- ----------------------------
INSERT INTO "main"."Course" VALUES (3001, '語(yǔ)文', 1001);
INSERT INTO "main"."Course" VALUES (3002, '數(shù)學(xué)', 1002);

-- ----------------------------
-- Table structure for Mark
-- ----------------------------
DROP TABLE IF EXISTS "main"."Mark";
CREATE TABLE Mark(
    userid integer,
    courseid integer not null,
    score int default 0
);

-- ----------------------------
-- Records of Mark
-- ----------------------------
INSERT INTO "main"."Mark" VALUES (2001, 3001, 89);
INSERT INTO "main"."Mark" VALUES (2001, 3002, 90);
INSERT INTO "main"."Mark" VALUES (2002, 3001, 66);
INSERT INTO "main"."Mark" VALUES (2003, 3002, 85);

-- ----------------------------
-- Table structure for sqlite_sequence
-- ----------------------------
DROP TABLE IF EXISTS "main"."sqlite_sequence";
CREATE TABLE sqlite_sequence(name,seq);

-- ----------------------------
-- Records of sqlite_sequence
-- ----------------------------
INSERT INTO "main"."sqlite_sequence" VALUES ('Teacher', 1002);
INSERT INTO "main"."sqlite_sequence" VALUES ('Student', 2002);
INSERT INTO "main"."sqlite_sequence" VALUES ('Course', 3002);

-- ----------------------------
-- Table structure for Student
-- ----------------------------
DROP TABLE IF EXISTS "main"."Student";
CREATE TABLE Student(
    userid integer  primary key autoincrement,
    username varchar(32),
    userage int,
    usersex varchar(32)
);

-- ----------------------------
-- Records of Student
-- ----------------------------
INSERT INTO "main"."Student" VALUES (2001, '小明', 18, '男');
INSERT INTO "main"."Student" VALUES (2002, '小紅', 18, '女');

-- ----------------------------
-- Table structure for Teacher
-- ----------------------------
DROP TABLE IF EXISTS "main"."Teacher";
CREATE TABLE Teacher(
    teacherid integer primary key autoincrement,
    teachername varchar(32)
);

-- ----------------------------
-- Records of Teacher
-- ----------------------------
INSERT INTO "main"."Teacher" VALUES (1001, '張三');
INSERT INTO "main"."Teacher" VALUES (1002, '李四');

問(wèn)題：

1、查詢“語(yǔ)文”課程比“數(shù)學(xué)”課程成績(jī)低的所有學(xué)生的學(xué)號(hào)

select a.userid from 
(select userid,score from Mark where courseid ='3001')a,
(select userid,score from Mark where courseid ='3002')b 
where a.userid = b.userid and a.score<b.score;

2、查詢平均成績(jī)大于60分的同學(xué)的學(xué)號(hào)和平均成績(jī)

select userid,avg(score) from Mark
group by userid 
having avg(score)>60;

3、查詢所有同學(xué)的學(xué)號(hào)、姓名、選課數(shù)、總成績(jī)

select s.userid ,s.username ,count_courseid as 選課數(shù), 
sum_score  as 總成績(jī)
from Student s
left join 
(select userid,count(courseid ) as count_courseid,sum(score) as sum_score 
from Mark group by userid  )sc
on s.userid = sc.userid;

4、查詢姓‘李'的老師的個(gè)數(shù)：

select count(teachername )
from Teacher 
where teachername  like '張%';

5、檢索語(yǔ)文課程分?jǐn)?shù)小于60，按分?jǐn)?shù)降序排列的同學(xué)學(xué)號(hào)：

select userid ,score
from Mark
where courseid ='3001'
and score<60
order by score desc;

6、查詢學(xué)/沒(méi)學(xué)過(guò)”張三”老師講授的任一門課程的學(xué)生姓名

select username  
from Student 
where userid  in (
    select userid  
    from Mark,Course,Teacher 
    where Course.teacherid  = Teacher.teacherid  and Mark.courseid = Course.courseid
    and Teacher.teachername ='張三'
);

7、查詢?nèi)繉W(xué)生選修的課程和課程號(hào)和課程名：

select courseid ,courseme 
from Course 
where courseid  in (select courseid from Mark group by courseid);

8、檢索選修兩門課程的學(xué)生學(xué)號(hào)：

select userid 
from Mark
group by userid 
having count(8) == 2;

9、查詢各個(gè)課程及相應(yīng)的選修人數(shù)

select courseid ,count(*) from Course group by courseid ;

10、查詢選修“張三”老師所授課程的學(xué)生中，成績(jī)最高的學(xué)生姓名及其成績(jī)

select Student.username ,Mark.score
from Mark 
left join Student  on Mark.userid = Student.userid 
left join Course  on Mark.courseid = Course.courseid 
left join Teacher  on Course.teacherid  = Teacher.teacherid 
where Teacher.teachername  = '張三'
and Mark.score = (
select max(score) 
from Mark sc_1 
where Mark.courseid = sc_1.courseid);

11、求選了課程的學(xué)生人數(shù)：

select count(2) from 
(select distinct userid from Mark)a;

12、查詢課程編號(hào)為“語(yǔ)文”且課程成績(jī)?cè)?0分以上的學(xué)生的學(xué)號(hào)和姓名

select Mark.userid,Student.username  
from Mark 
left join Student on Mark.userid  = Student.userid 
where Mark.courseid  = '3001' and Mark.score>80;

13、查詢每門課程的平均成績(jī)，結(jié)果按平均成績(jī)升序排序，平均成績(jī)相同時(shí)，按課程號(hào)降序排列

select courseid ,avg(score)
from Mark 
group by courseid 
order by avg(score),courseid desc;

14、查詢課程名稱為“數(shù)學(xué)”，且分?jǐn)?shù)高于85的學(xué)生名字和分?jǐn)?shù)：

select c.courseme ,Student.userid ,Student.username ,Mark.score
from Course c
left join Mark on Mark.courseid  = c.courseid 
LEFT JOIN Student  on Student.userid  = Mark.userid 
where c.courseme = '數(shù)學(xué)' and Mark.score>85;

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