MySQL多表連接項目案例實踐 老男孩Linux運維MySQL課程
（1）准備工作（表名和表結構）
use school student ：學生表 sno： 學號 sname：學生姓名 sage： 學生年齡 ssex： 學生性別 teacher ：教師表 tno： 教師編號 tname： 教師名字 course ：課程表 cno： 課程編號 cname：課程名字 tno： 教師編號 score ：成績表 sno： 學號 cno： 課程編號 score：成績
（2）各個表關聯關系
（3）生成表格及插入數據
/* oldboyedu.com by oldboy
Date: 05/12/2021 10:32:02 */
SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;
create database school CHARSET=utf8mb4;
use school;
-- ----------------------------
-- Table structure for course
-- ----------------------------
DROP TABLE IF EXISTS `course`;
CREATE TABLE `course` (
`cno` int(11) NOT NULL COMMENT '課程編號',
`cname` varchar(20) NOT NULL COMMENT '課程名字',
`tno` int(11) NOT NULL COMMENT '教師編號',
PRIMARY KEY (`cno`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
-- ----------------------------
-- Records of course
-- ----------------------------
BEGIN;
INSERT INTO `course` VALUES (1001, 'linux', 101);
INSERT INTO `course` VALUES (1002, 'python', 102);
INSERT INTO `course` VALUES (1003, 'mysql', 103);
INSERT INTO `course` VALUES (1004, 'k8s', 108);
COMMIT;
-- ----------------------------
-- Table structure for sc
-- ----------------------------
DROP TABLE IF EXISTS `sc`;
CREATE TABLE `sc` (
`sno` int(11) NOT NULL COMMENT '學號',
`cno` int(11) NOT NULL COMMENT '課程編號',
`score` int(11) NOT NULL DEFAULT '0' COMMENT '成績'
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
-- ----------------------------
-- Records of sc
-- ----------------------------
BEGIN;
INSERT INTO `sc` VALUES (1, 1001, 80);
INSERT INTO `sc` VALUES (1, 1002, 59);
INSERT INTO `sc` VALUES (2, 1002, 90);
INSERT INTO `sc` VALUES (2, 1003, 100);
INSERT INTO `sc` VALUES (3, 1001, 99);
INSERT INTO `sc` VALUES (3, 1003, 40);
INSERT INTO `sc` VALUES (4, 1001, 79);
INSERT INTO `sc` VALUES (4, 1002, 61);
INSERT INTO `sc` VALUES (4, 1003, 99);
INSERT INTO `sc` VALUES (5, 1003, 40);
INSERT INTO `sc` VALUES (6, 1001, 89);
INSERT INTO `sc` VALUES (6, 1003, 77);
INSERT INTO `sc` VALUES (7, 1001, 67);
INSERT INTO `sc` VALUES (7, 1003, 82);
INSERT INTO `sc` VALUES (8, 1001, 70);
INSERT INTO `sc` VALUES (9, 1003, 80);
INSERT INTO `sc` VALUES (10, 1003, 96);
COMMIT;
-- ----------------------------
-- Table structure for student
-- ----------------------------
DROP TABLE IF EXISTS `student`;
CREATE TABLE `student` (
`sno` int(11) NOT NULL AUTO_INCREMENT COMMENT '學號',
`sname` varchar(20) NOT NULL COMMENT '姓名',
`sage` tinyint(3) unsigned NOT NULL COMMENT '年齡',
`ssex` enum('f','m') NOT NULL DEFAULT 'm' COMMENT '性別',
PRIMARY KEY (`sno`)
) ENGINE=InnoDB AUTO_INCREMENT=11 DEFAULT CHARSET=utf8mb4;
-- ----------------------------
-- Records of student
-- ----------------------------
BEGIN;
INSERT INTO `student` VALUES (1, 'zhangs', 18, 'm');
INSERT INTO `student` VALUES (2, 'lisi88', 18, 'm');
INSERT INTO `student` VALUES (3, 'wangwu', 22, 'm');
INSERT INTO `student` VALUES (4, 'laoliu', 19, 'f');
INSERT INTO `student` VALUES (5, 'zhao4m', 18, 'm');
INSERT INTO `student` VALUES (6, 'liuxia', 18, 'm');
INSERT INTO `student` VALUES (7, 'matian', 19, 'f');
INSERT INTO `student` VALUES (8, 'oldboy', 20, 'm');
INSERT INTO `student` VALUES (9, 'oldgirl', 20, 'f');
INSERT INTO `student` VALUES (10, 'oldpod', 25, 'm');
COMMIT;
-- ----------------------------
-- Table structure for teacher
-- ----------------------------
DROP TABLE IF EXISTS `teacher`;
CREATE TABLE `teacher` (
`tno` int(11) NOT NULL COMMENT '教師編號',
`tname` varchar(20) NOT NULL COMMENT '教師名字',
PRIMARY KEY (`tno`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
-- ----------------------------
-- Records of teacher
-- ----------------------------
BEGIN;
INSERT INTO `teacher` VALUES (101, 'oldboy');
INSERT INTO `teacher` VALUES (102, 'ran');
INSERT INTO `teacher` VALUES (103, 'lisir');
INSERT INTO `teacher` VALUES (104, 'Tim');
INSERT INTO `teacher` VALUES (105, 'Jack');
COMMIT;
SET FOREIGN_KEY_CHECKS = 1;
項目構建：
source /root/school.sql
（4）多表連接查詢數據實踐
#實踐練習
#1.統計下每個學生的平均成績
解答：
#a.分析題意,找出所有相關表student、sc
#b.找到以上表的直接或間接關聯條件，student.sno，sc.sno
#c.列舉要查詢的列條件，student.sname，sc.score
#d.組合最終結果：
mysql> SELECT student.sname,AVG(sc.score) FROM student JOIN sc ON student.sno=sc.sno GROUP BY student.sno;
+---------+---------------+
| sname | AVG(sc.score) |
+---------+---------------+
| zhangs | 69.5000 |
| lisi88 | 95.0000 |
...省略若干行...
| oldgirl | 80.0000 |
| oldpod | 96.0000 |
+---------+---------------+
#2.統計每位學生學習的課程門數
mysql> SELECT student.sname,COUNT(sc.score) FROM student JOIN sc ON student.sno=sc.sno GROUP BY student.sno;
+---------+-----------------+
| sname | COUNT(sc.score) |
+---------+-----------------+
| zhangs | 2 |
| lisi88 | 2 |
...省略若干行...
| oldgirl | 1 |
| oldpod | 1 |
+---------+-----------------+
#3.統計每位老師所教的課程門數
mysql> SELECT teacher.tname ,COUNT(course.cname) FROM teacher JOIN course ON teacher.tno=course.tno GROUP BY teacher.tno;
+--------+---------------------+
| tname | COUNT(course.cname) |
+--------+---------------------+
| oldboy | 1 |
| ran | 1 |
| lisir | 1 |
+--------+---------------------+
#4.每位老師所教的課程門數和名稱
mysql> SELECT teacher.tname ,COUNT(course.cname),GROUP_CONCAT(course.cname)
-> FROM teacher JOIN course ON teacher.tno=course.tno
-> GROUP BY teacher.tno;
+--------+---------------------+----------------------------+
| tname | COUNT(course.cname) | GROUP_CONCAT(course.cname) |
+--------+---------------------+----------------------------+
| oldboy | 1 | linux |
| ran | 1 | python |
| lisir | 1 | mysql |
+--------+---------------------+----------------------------+
#5.每位學生學習的課程門數和名稱
mysql> SELECT student.sname,COUNT(sc.score),GROUP_CONCAT(course.cname)
-> FROM student
-> JOIN sc
-> ON student.sno=sc.sno
-> JOIN course
-> ON sc.cno=course.cno
-> GROUP BY student.sno;
+---------+-----------------+----------------------------+
| sname | COUNT(sc.score) | GROUP_CONCAT(course.cname) |
+---------+-----------------+----------------------------+
| zhangs | 2 | python,linux |
...省略若干行...
| oldboy | 1 | linux |
| oldgirl | 1 | mysql |
| oldpod | 1 | mysql |
+---------+-----------------+----------------------------+
（5）多表SQL考試題
1. 統計zhangs,學習了幾門課
2. 查詢zhangs,學習的課程名稱有哪些?
3. 查詢oldboy老師教的學生名.
4. 查詢oldboy所教課程的平均分數
5. 每位老師所教課程的平均分,並按平均分排序
6. 查詢ran所教的不及格的學生姓名
7. 查詢所有老師所教學生不及格的信息
8. 查詢平均成績大於60分的同學的學號和平均成績；
9. 查詢所有同學的學號、姓名、選課數、總成績；
10.查詢各科成績最高和最低的分：以如下形式顯示：課程ID，最高分，最低分
11.查詢每門課程被選修的學生數
12.查詢出只選修了一門課程的全部學生的學號和姓名
13.查詢選修課程門數超過1門的學生信息
14.查詢平均成績大於85的所有學生的學號、姓名和平均成績
15.統計各位老師,所教課程的及格率
16.統計每門課程:優秀(85分以上),良好(70-85),一般(60-70),不及格(小於60)的學生列表
《本內容來自老男孩教育MySQL部分教學》，交流數據庫技術可加右上角聯系方式