CREATE TABLE lovostudebt(
studentCode VARCHAR(20) PRIMARY KEY,
studentName VARCHAR(20),
age INT,
sex VARCHAR(10),
grade INT,
clasddName VARCHAR (20)
)DEFAULT CHARSET=utf8;
INSERT INTO lovostudebt (studentCode,studentName,age,sex,grade,clasddName)
VALUES(\'xh1001\',\'jacky\',\'20\',\'男\',\'90\',\'T01\'),
(\'xh1002\',\'simth\',\'30\',\'男\',\'75\',\'T02\'),
(\'xh1003\',\'jay\',\'18\',\'男\',\'80\',\'T01\'),
(\'xh1004\',\'helen\',\'19\',\'女\',\'75\',\'T02\'),
(\'xh1005\',\'lily\',\'22\',\'女\',\'90\',\'T03\'),
(\'xh1006\',\'Green\',\'23\',\'男\',\'85\',\'T02\'),
(\'xh1007\',\'RedChar\',\'18\',\'男\',\'60\',\'T01\'),
(\'xh1008\',\'Kevin\',\'17\',\'女\',\'45\',\'T03\');
SELECT *FROM lovostudebt;
DROP TABLE lovostudebt;
-- 得到所有学生的总分 sum 表示求和
SELECT SUM(grade) AS \'总分\' FROM lovostudebt;
-- 等到所有学生的最高分 max 表示求最大值
SELECT MAX(grade) AS \'最高分\' FROM lovostudebt;
-- 得到所有学生的最低分，min表示求最小值
SELECT MIN(grade) AS\'最低分\' FROM lovostudebt;
-- 得到所有学生的平均分 ，avg表示求平均分
SELECT AVG(grade) AS\'平均分\' FROM lovostudebt;
-- 得到所有学生的总人数
-- COUNT (geade)同级总人数，会忽略该列为null的记录。
-- COUNT (*)不会忽略该列为null的记录。
SELECT COUNT(grade)AS\'人数\' FROM lovostudebt;
SELECT COUNT(*)AS\'人数\' FROM lovostudebt;
-- 分组查询每个班级的总分
-- GROUP BY 是以什么进行分组
SELECT clasddName,SUM(grade) AS\'总分\' FROM lovostudebt GROUP BY clasddName;
-- 分组查询每个班级的平均分 最高分 最低分 参考人数
-- clasddName 班级名称
-- 分组之后在select 中出现的字段，织女呢个是分组字段（group by 后面的字段）或者是聚合函数
SELECT clasddName,SUM(grade) AS\'总分\',
AVG(grade) AS\'平均分\',
MAX(grade) AS \'最高分\',
MIN(grade) AS\'最低分\',
COUNT(grade) AS\'参考人数\'
FROM lovostudebt GROUP BY clasddName;
-- 查询平均分在85以上的学生
-- where 后面不能跟聚合函数,因为where执行在GROUP by之前
-- having 执行在分组之后，可以跟聚合函数
SELECT clasddName FROM lovostudebt GROUP BY clasddName HAVING AVG(grade)>=75;
-- 查询那个班有女生，并说出女生的人数
SELECT clasddName AS\'班级名称\',COUNT(sex) AS \'女生人数\' FROM lovostudebt WHERE sex=\'女\' GROUP BY clasddName;
CREATE TABLE student(
id INT PRIMARY KEY AUTO_INCREMENT,
studentCode INT, -- 学号
studentName VARCHAR(20), -- 学生成绩
subjectName VARCHAR(20),
grade INT, -- 成绩
classID INT -- 班级编号
)DEFAULT CHARSET=utf8;
CREATE TABLE class(
id INT PRIMARY KEY AUTO_INCREMENT,
className VARCHAR (20) -- 班级
)DEFAULT CHARSET=utf8;
-- 增加外键约束
ALTER TABLE student ADD CONSTRAINT fk_class FOREIGN KEY (classID) REFERENCES class(id);
INSERT INTO class (className) VALUES(\'T01\'),(\'T02\'),(\'T03\'),(\'T04\');
SELECT *FROM class;
DROP TABLE class;
INSERT INTO student(studentCode, studentName,subjectName,grade,classID )
VALUES(1,\'张三\',\'计算机基础\',60,1),
(1,\'张三\',\'C语言\',88,1),
(1,\'张三\',\'关系型数据库基础\',90,1),
(2,\'王五\',\'计算机基础\',80,2),
(2,\'王五\',\'C语言\',70,2),
(2,\'王五\',\'关系型数据库基础\',55,2),
(3,\'李四\',\'C语言\',66,4),
(3,\'李四\',\'关系型数据库基础\',90,4);
SELECT* FROM student;
DROP TABLE student;
-- 显示C语言这门课程的最高分和得最高分的学生姓名
SELECT MAX(grade),studentName FROM student WHERE subjectName=\'计算机基础\'
AND grade=(SELECT MAX(grade) FROM student WHERE subjectName=\'计算机基础\');
SELECT * FROM student WHERE subjectName=\'计算机基础\' ORDER BY grade DESC LIMIT 0,1;
-- 显示所有学生信息，要求将班级编号转化为班级名称
SELECT s.*,(SELECT className FROM class AS c WHERE c.id = s.classID) AS\'班级名称\' FROM student AS s;
-- 查询比王五c语言考得更好的学生
SELECT * FROM student WHERE subjectName =\'c语言\' AND
grade >(SELECT grade FROM student WHERE subjectName=\'c语言\' AND studentName=\'王五\');
-- 查询关系型数据库和张三同分的学生信息
SELECT *FROM student WHERE subjectName =\'关系型数据库基础\' AND
grade=(SELECT grade FROM student WHERE subjectName =\'关系型数据库基础\'
AND studentName=\'张三\' )AND studentName!=\'张三\';
-- 查询那个班级有学生
SELECT className FROM class WHERE id IN (SELECT DISTINCT classID FROM student);
-- 查询那个班级没有学生
SELECT className FROM class WHERE id NOT IN (SELECT DISTINCT classID FROM student);
-- 找出每门课程的最高分和学生姓名
SELECT * FROM student s1 WHERE grade IN(
SELECT MAX(grade) FROM student s2
WHERE s1.subjectName=s2.subjectName GROUP BY subjectName);
-- 查询所有学生姓名、科目、成绩、所在班级
SELECT s.studentName,s.subjectName,s.grade,c.className FROM
student s JOIN class c ON s.classID=c.id;
SELECT s.studentName,s.subjectName,s.grade,c.className FROM
student s ,class c WHERE s.classID=c.id;
CREATE TABLE t_student(
id INT PRIMARY KEY AUTO_INCREMENT,
StudentName VARCHAR (20),
chinese INT,
math INT,
english INT,
cardCode VARCHAR (20) -- 考试号
)DEFAULT CHARSET=utf8;
INSERT INTO t_student(StudentName,chinese,math,english,cardCode)
VALUES(\'张无忌\',\'90\',\'80\',\'70\',\'12121525121\'),
(\'王振天\',\'44\',\'88\',\'74\',\'12454545551\'),
(\'胡凯\',\'73\',\'58\',\'99\',\'11245454545\'),
(\'李金\',\'70\',\'90\',\'84\',\'52524645254\');
SELECT*FROM t_student;
DROP TABLE t_student;
-- 将张无忌的语文更改为95分，数学改为85分，
UPDATE t_student SET chinese=\'95\',math=\'85\' WHERE StudentName= \'张无忌\'; -- 可以换成ID
-- 将数学成绩都加5分
UPDATE t_student SET math=math+5;
-- 将姓张的人英语减10分
-- 张%，表示通配符，匹配张开始的所有字符串（张三，张四，张五）
-- %张%，表示（刘张云，杨张云）
UPDATE t_student SET english=english-10 WHERE StudentName LIKE \'张%\'
-- 增加学校列
ALTER TABLE t_student ADD school VARCHAR(30);
-- 修改张无忌的学校为成都十二中，胡凯学校为成都七中
UPDATE t_student SET school=\'成都十二中\' WHERE id=1;
UPDATE t_student SET school=\'成都七中\' WHERE id=3;
-- 修改学校为null的记录，学校更改为成都四中
UPDATE t_student SET school=\'成都四中\' WHERE school IS NULL;
-- 删除胡凯
DELETE FROM t_student WHERE studentName=\'胡凯\';
-- 删除60-70之间的记录
DELETE FROM t_student WHERE english>=60 AND english<=70;
-- 也可以写成
DELETE FROM t_student WHERE english BETWEEN 60 AND 70;
-- 删除所有
TRUNCATE TABLE t_student;
-- 查询所有记录
-- *表示该表中所有的字段
SELECT * FROM t_student;
-- 查询所有学生的姓名和语文成绩
SELECT studentName,chinese FROM t_student;
-- AS表示给该列取别名
SELECT studentName AS\'姓名\',chinese AS \'语文\' FROM t_student;
-- DISTINCT 去除重复的记录
SELECT DISTINCT school FROM t_student;