MySQL 查詢數據練習 20191010

測試數據：

DROP TABLE IF EXISTS `student`;
CREATE  TABLE  student (
id  INT(10)  NOT NULL  UNIQUE  PRIMARY KEY  ,
NAME  VARCHAR(20)  NOT NULL ,
sex  VARCHAR(4)  ,
birth  YEAR,
department  VARCHAR(20) ,
address  VARCHAR(50) 
);
CREATE  TABLE  score (

id  INT(10)  NOT NULL  UNIQUE  PRIMARY KEY  AUTO_INCREMENT ,

stu_id  INT(10)  NOT NULL ,

c_name  VARCHAR(20) ,

grade  INT(10)

);
INSERT INTO student VALUES( 901,'張老大', '男',1985,'計算機系', '北京市海淀區');

INSERT INTO student VALUES( 902,'張老二', '男',1986,'中文系', '北京市昌平區');

INSERT INTO student VALUES( 903,'張三', '女',1990,'中文系', '湖南省永州市');

INSERT INTO student VALUES( 904,'李四', '男',1990,'英語系', '遼寧省阜新市');

INSERT INTO student VALUES( 905,'王五', '女',1991,'英語系', '福建省廈門市');

INSERT INTO student VALUES( 906,'王六', '男',1988,'計算機系', '湖南省衡陽市');

INSERT INTO score VALUES(NULL,901, '計算機',98);

INSERT INTO score VALUES(NULL,901, '英語', 80);

INSERT INTO score VALUES(NULL,902, '計算機',65);

INSERT INTO score VALUES(NULL,902, '中文',88);

INSERT INTO score VALUES(NULL,903, '中文',95);

INSERT INTO score VALUES(NULL,904, '計算機',70);

INSERT INTO score VALUES(NULL,904, '英語',92);

INSERT INTO score VALUES(NULL,905, '英語',94);

INSERT INTO score VALUES(NULL,906, '計算機',90);

INSERT INTO score VALUES(NULL,906, '英語',85);

3.查詢student表的所有記錄
查詢student表的第2條到4條記錄
5.從student表查詢所有學生的學號（id）、姓名（name）和院系（department）的信息
從student表中查詢計算機系和英語系的學生的信息
從student表中查詢年齡18~22歲的學生信息
從student表中查詢每個院系有多少人
9.從score表中查詢每個科目的最高分
10.查詢李四的考試科目（c_name）和考試成績（grade）
11.用連接的方式查詢所有學生的信息和考試信息
12.計算每個學生的總成績
13.計算每個考試科目的平均成績
14.查詢計算機成績低於95的學生信息
15.查詢同時參加計算機和英語考試的學生的信息
16.將計算機考試成績按從高到低進行排序
18.查詢姓張或者姓王的同學的姓名、院系和考試科目及成績
19.查詢都是湖南的學生的姓名、年齡、院系和考試科目及成績

SELECT * FROM student;
SELECT * FROM student LIMIT 1,3;
SELECT id AS 學號,NAME AS 姓名, department AS 系別 FROM student;
SELECT * FROM student WHERE department IN ('中文系','計算機系');
SELECT * FROM student WHERE department = '中文系' OR department ='計算機系';
SELECT * FROM student WHERE department LIKE '中文系' OR department ='計算機系';
SELECT * FROM student WHERE birth BETWEEN 1991 AND 1996;
SELECT id,NAME,sex,2013-birth AS age,department,address FROM student WHERE 2013-birth BETWEEN  18 AND 22;
SELECT id,NAME,sex,2013-birth AS age,department,address FROM student WHERE 2013-birth>=18 AND 2013-birth<=22;
SELECT department,COUNT(*) AS 人數 FROM student GROUP BY department;
SELECT * FROM student AS st INNER JOIN score AS sc ON st.id = sc.stu_id;
SELECT  stu_id,SUM(grade) FROM score GROUP BY stu_id;
SELECT  student.id ,SUM(score.grade) FROM student,score WHERE student.id = score.stu_id GROUP BY student.id;
SELECT a.stu_id, AVG(a.grade + b.grade)  FROM score a,score b WHERE a.stu_id = b.stu_id  GROUP BY a.stu_id;
SELECT c_name,AVG(grade) FROM score GROUP BY c_name;
SELECT st.id,st.name,sc.c_name FROM student AS st LEFT JOIN  score AS sc ON sc.stu_id = st.id AND sc.c_name = "計算機" AND sc.c_name = "英語";


##查詢都是湖南的學生的姓名、年齡、院系和考試科目及成績
```sql
SELECT st.name,st.department,sc.c_name,sc.grade,st.address FROM student AS st INNER JOIN score AS sc ON st.address LIKE "湖南省%" AND sc.stu_id = st.id ;
SELECT st.name,st.department,sc.c_name,sc.grade,st.address FROM student AS st LEFT OUTER JOIN score AS sc ON sc.stu_id = st.id WHERE st.address LIKE "湖南省%" ;
SELECT st.name,st.department,GROUP_CONCAT(sc.c_name),GROUP_CONCAT(sc.grade),st.address FROM student AS st LEFT OUTER JOIN score AS sc ON sc.stu_id = st.id WHERE st.address LIKE "湖南省%" GROUP BY st.name  ;