mysql基础练习题

一、表关系

请创建如下表，并创建相关约束

二、操作表

1、自行创建测试数据

/*
Navicat MySQL Data Transfer
 
Source Server         : mysql5.7.1
Source Server Version : 50717
Source Host           : localhost:3306
Source Database       : crm
 
Target Server Type    : MYSQL
Target Server Version : 50717
File Encoding         : 65001
 
Date: 2017-02-24 09:50:15
*/
 
SET FOREIGN_KEY_CHECKS=0;
 
-- ----------------------------
-- Table structure for class
-- ----------------------------
DROP TABLE IF EXISTS `class`;
CREATE TABLE `class` (
  `cid` int(11) NOT NULL AUTO_INCREMENT,
  `caption` varchar(32) NOT NULL,
  PRIMARY KEY (`cid`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
 
-- ----------------------------
-- Records of class
-- ----------------------------
INSERT INTO `class` VALUES ('', '三年二班');
INSERT INTO `class` VALUES ('', '三年三班');
INSERT INTO `class` VALUES ('', '一年二班');
INSERT INTO `class` VALUES ('', '二年九班');
 
-- ----------------------------
-- Table structure for course
-- ----------------------------
DROP TABLE IF EXISTS `course`;
CREATE TABLE `course` (
  `cid` int(11) NOT NULL AUTO_INCREMENT,
  `cname` varchar(32) NOT NULL,
  `teacher_id` int(11) NOT NULL,
  PRIMARY KEY (`cid`),
  KEY `fk_course_teacher` (`teacher_id`),
  CONSTRAINT `fk_course_teacher` FOREIGN KEY (`teacher_id`) REFERENCES `teacher` (`tid`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
 
-- ----------------------------
-- Records of course
-- ----------------------------
INSERT INTO `course` VALUES ('', '生物', '');
INSERT INTO `course` VALUES ('', '物理', '');
INSERT INTO `course` VALUES ('', '体育', '');
INSERT INTO `course` VALUES ('', '美术', '');
 
-- ----------------------------
-- Table structure for score
-- ----------------------------
DROP TABLE IF EXISTS `score`;
CREATE TABLE `score` (
  `sid` int(11) NOT NULL AUTO_INCREMENT,
  `student_id` int(11) NOT NULL,
  `course_id` int(11) NOT NULL,
  `num` int(11) NOT NULL,
  PRIMARY KEY (`sid`),
  KEY `fk_score_student` (`student_id`),
  KEY `fk_score_course` (`course_id`),
  CONSTRAINT `fk_score_course` FOREIGN KEY (`course_id`) REFERENCES `course` (`cid`),
  CONSTRAINT `fk_score_student` FOREIGN KEY (`student_id`) REFERENCES `student` (`sid`)
) ENGINE=InnoDB AUTO_INCREMENT=53 DEFAULT CHARSET=utf8;
 
-- ----------------------------
-- Records of score
-- ----------------------------
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
INSERT INTO `score` VALUES ('', '', '', '');
 
-- ----------------------------
-- Table structure for student
-- ----------------------------
DROP TABLE IF EXISTS `student`;
CREATE TABLE `student` (
  `sid` int(11) NOT NULL AUTO_INCREMENT,
  `gender` char(1) NOT NULL,
  `class_id` int(11) NOT NULL,
  `sname` varchar(32) NOT NULL,
  PRIMARY KEY (`sid`),
  KEY `fk_class` (`class_id`),
  CONSTRAINT `fk_class` FOREIGN KEY (`class_id`) REFERENCES `class` (`cid`)
) ENGINE=InnoDB AUTO_INCREMENT=17 DEFAULT CHARSET=utf8;
 
-- ----------------------------
-- Records of student
-- ----------------------------
INSERT INTO `student` VALUES ('', '男', '', '刘洋');
INSERT INTO `student` VALUES ('', '女', '', '钢蛋');
INSERT INTO `student` VALUES ('', '男', '', '刘泽栋');
INSERT INTO `student` VALUES ('', '男', '', '张少博');
INSERT INTO `student` VALUES ('', '女', '', '张少强');
INSERT INTO `student` VALUES ('', '男', '', '王飞');
INSERT INTO `student` VALUES ('', '女', '', '铁锤');
INSERT INTO `student` VALUES ('', '男', '', '李三');
INSERT INTO `student` VALUES ('', '男', '', '李一');
INSERT INTO `student` VALUES ('', '女', '', '李二');
INSERT INTO `student` VALUES ('', '男', '', '李四');
INSERT INTO `student` VALUES ('', '女', '', '王鹏');
INSERT INTO `student` VALUES ('', '男', '', '刘明');
INSERT INTO `student` VALUES ('', '男', '', '刘刚');
INSERT INTO `student` VALUES ('', '女', '', '刘二');
INSERT INTO `student` VALUES ('', '男', '', '刘四');
 
-- ----------------------------
-- Table structure for teacher
-- ----------------------------
DROP TABLE IF EXISTS `teacher`;
CREATE TABLE `teacher` (
  `tid` int(11) NOT NULL AUTO_INCREMENT,
  `tname` varchar(32) NOT NULL,
  PRIMARY KEY (`tid`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8;
 
-- ----------------------------
-- Records of teacher
-- ----------------------------
INSERT INTO `teacher` VALUES ('', '马云老师');
INSERT INTO `teacher` VALUES ('', '刘强东老师');
INSERT INTO `teacher` VALUES ('', '马化腾老师');
INSERT INTO `teacher` VALUES ('', '丁磊老师');
INSERT INTO `teacher` VALUES ('', '王建宁老师');
INSERT INTO `teacher` VALUES ('', '李杰老师');

2、操作

--
-- 1、自行创建测试数据
--
-- 2、查询“生物”课程比“物理”课程成绩高的所有学生的学号；
-- SELECT
-- 	A.student_id,A.num
-- FROM
-- 	(
-- 		SELECT
-- 			score.sid,
-- 			score.student_id,
-- 			course.cname,
-- 			score.num
-- 		FROM
-- 			score
-- 		LEFT JOIN course ON score.course_id = course.cid
-- 		WHERE
-- 			course.cname = "生物"
-- 	) AS A
--
-- INNER JOIN (
--
-- SELECT
-- 		score.sid,
-- 		score.student_id,
-- 		course.cname,
-- 		score.num
-- 	FROM
-- 		score
-- 	LEFT JOIN course ON score.course_id = course.cid
-- 	WHERE
-- 		course.cname = "物理"
-- ) AS B ON A.student_id = B.student_id
-- WHERE
-- 	A.num > B.num --
 
-- 3、查询平均成绩大于60分的同学的学号和平均成绩；
-- SELECT
-- 	B.student_id,
-- 	student.sname,
-- 	B.aa
-- FROM
-- 	(
-- 		SELECT
-- 			student_id,
-- 			avg(num) AS aa
-- 		FROM
-- 			score
-- 		GROUP BY
-- 			student_id
-- 		HAVING
-- 			avg(num) > 60
-- 	) AS B
-- LEFT JOIN student ON B.student_id = student.sid
 
-- 4、查询所有同学的学号、姓名、选课数、总成绩；
--  SELECT
-- 	score.student_id,
--  	count(course_id),
-- 	student.sname,
--  	sum(num)
--  FROM
--  	score
--  LEFT JOIN student ON score.student_id = student.sid
--  GROUP BY
--  	score.student_id;
--
--
-- 5、查询姓“李”的老师的个数；
-- select tid from teacher where tname like '李%';
--
-- 6、查询没学过“李平”老师课的同学的学号、姓名；
--  SELECT
-- 			 	student.sid,
-- 			 	student.sname
-- 			 FROM
-- 			 	student
-- 		 WHERE
-- 			sid NOT IN (
-- 				SELECT
-- 						student_id
-- 				FROM
-- 						score
-- 					WHERE
-- 		 			course_id IN (
-- 		 				SELECT
-- 			 					course.cid
-- 			 				FROM
-- 		 					course
-- 		 				LEFT JOIN teacher ON course.teacher_id = teacher.tid
-- 			 				WHERE
-- 								teacher.tname = "李平老师"
-- 			 			)
-- 			 		GROUP BY
-- 		 			student_id
-- 		 	)
--
--
-- 7、查询学过“001”并且也学过编号“002”课程的同学的学号、姓名；
-- SELECT
-- 	student_id,
-- 	student.sname
-- FROM
-- 	(
-- 		SELECT
-- 			student_id,
-- 			course_id
-- 		FROM
-- 			score
-- 		WHERE
-- 			score.course_id = 1
-- 		OR score.course_id = 2
-- 	) AS A
-- LEFT JOIN student ON A.student_id = student.sid
-- GROUP BY
-- 	student_id
-- HAVING
-- 	count(student_id) > 1;
-- 
 
-- 8、查询学过“李平”老师所教的所有课的同学的学号、姓名；
 
-- SELECT
-- 	student_id
-- FROM
-- 	score
-- WHERE
-- 	course_id IN (
-- 		SELECT
-- 			cid
-- 		FROM
-- 			course
-- 		LEFT JOIN teacher ON teacher_id = teacher.tid
-- 		WHERE
-- 			teacher.tname = "李平老师"
-- 	)
-- GROUP BY
-- 	student_id
-- HAVING
-- 	count(course_id) = (
-- 		SELECT
-- 			count(cid)
-- 		FROM
-- 			course
-- 		LEFT JOIN teacher ON teacher_id = teacher.tid
-- 		WHERE
-- 			teacher.tname = "李平老师"
-- 	)
-- 
 
-- 9、查询课程编号“002”的成绩比课程编号“001”课程低的所有同学的学号、姓名；
--  SELECT
--
-- A.student_id,A.num
--   FROM
--  	(
--  		SELECT
--  			score.sid,
--   			score.student_id,
-- 			score.course_id,
-- 			score.num
--  		FROM
-- 			score
--  		LEFT JOIN course ON score.course_id = course.cid
--  		WHERE
--  			score.course_id = 1
--   	) AS A
--
--   INNER JOIN
--
--  (
--  	SELECT
--   		score.sid,
-- 		score.student_id,
--  		score.course_id,
-- 		score.num
--   	FROM
--   		score
--   	LEFT JOIN course ON score.course_id = course.cid
--   	WHERE
--  		score.course_id = 2)
--
--   AS B ON A.student_id = B.student_id
--   WHERE
-- 	A.num > B.num
-- 
 
-- 10、查询有课程成绩小于60分的同学的学号、姓名；
--
-- SELECT
-- 	score.student_id,
-- 	student.sname
-- FROM
-- 	score
-- LEFT JOIN student ON score.student_id = student.sid
-- WHERE
-- 	score.num < 60
-- GROUP BY
-- 	student_id;
 
--
-- 11、查询没有学全所有课的同学的学号、姓名；
--   select
--  	student_id,
--   	student.sname
--   FROM
--   	score
--   LEFT JOIN student ON score.student_id = student.sid
--   GROUP BY
--  	score.student_id
--   HAVING count(1) < (select count(cid) from course);
--
--
-- 12、查询至少有一门课与学号为“001”的同学所学相同的同学的学号和姓名；
-- SELECT
-- 	student_id,
-- 	student.sname
-- FROM
-- 	score
-- LEFT JOIN student ON score.student_id = student.sid
-- WHERE
-- 	student_id != 1
-- AND course_id IN (
-- 	SELECT
-- 		course_id
-- 	FROM
-- 		score
-- 	WHERE
-- 		student_id = 1
-- )
-- GROUP BY
-- student_id
 
-- 13、查询至少学过学号为“001”同学所选课程中任意一门课的其他同学学号和姓名；
-- select course_id from score where  student_id=1;
 
-- SELECT
-- 	student_id,
-- 	count(1)
-- FROM
-- 	score
-- WHERE
-- 	student_id != 1
-- AND course_id IN (
-- 	SELECT
-- 		course_id
-- 	FROM
-- 		score
-- 	WHERE
-- 		student_id = 1
-- )
-- GROUP BY
-- 	student_id
-- HAVING
-- 	count(1) = (
-- 		SELECT
-- 			count(course_id)
-- 		FROM
-- 			score
-- 		WHERE
-- 			student_id = 1
-- 	)
-- 
 
-- 14、查询和“002”号的同学学习的课程完全相同的其他同学学号和姓名；
 
--  select count(1) from score where student_id=1;
 
-- select student_id,sname from score LEFT JOIN student on score.student_id=student.sid where student_id in (
--
--   select student_id from score where student_id !=1 GROUP BY student_id HAVING count(1)=(select count(1) from score where student_id=1)
--
-- )and course_id in(select course_id from score where student_id=1) GROUP BY student_id having count(1) =(select count(1) from score where student_id=1);
--
-- 
 
-- 15、删除学习“李平”老师课的SC表记录；
--  DELETE
-- FROM
--  	score
--  WHERE
-- 	course_id IN (
--  		SELECT
--  			cid
-- 		FROM
--  			course
-- 		LEFT JOIN teacher ON course.teacher_id = teacher.tid
--  		WHERE
--  			teacher.tname = "李平"
--  	)
--
--
-- 16、向SC表中插入一些记录，这些记录 要求符合以下条件：①没有上过编号“002”课程的同学学号；②插入“002”号课程的平均成绩； 
 
-- 插入表格 insert into tb(student_id,course_id,num) 映射里面加动态值 
 
--  select student_id from score where course_id!=2
 
-- SELECT
-- 	student_id,
-- 	2,
-- 	(
-- 		SELECT
-- 			AVG(num)
-- 		FROM
-- 			score
-- 		WHERE
-- 			course_id = 2
-- 	)
-- FROM
-- 	score
-- WHERE
-- 	course_id != 2 
 
-- 17、按平均成绩从低到高显示所有学生的“语文”、“数学”、“英语”三门的课程成绩，按如下形式显示： 学生ID,语文,数学,英语,有效课程数,有效平均分；
 
-- select student_id,
--    (select num from score as s2 where s2.student_id=s1.student_id and course_id=1)as 语文,
--    (select num from score as s2 where s2.student_id=s1.student_id and course_id=1)as 数学,
--    (select num from score as s2 where s2.student_id=s1.student_id and course_id=1)as 英语
-- from score as s1;
--
--
-- 18、查询各科成绩最高和最低的分：以如下形式显示：课程ID，最高分，最低分；
 
-- SELECT
-- 	course_id,
-- 	MAX(num),
-- 	min(num)
-- FROM
-- 	score
-- GROUP BY
-- 	course_id
-- 
 
-- 19、按各科平均成绩从低到高和及格率的百分数从高到低顺序；
-- 运用了 case when xx then xx else xx 判断语句
 
-- SELECT
-- 	course_id,
-- 	avg(num),
-- 	sum(
-- 		CASE
-- 		WHEN num < 60 THEN
-- 			0
-- 		ELSE
-- 			1
-- 		END
-- 	),
-- 	sum(1),
-- 	sum(
-- 		CASE
-- 		WHEN num < 60 THEN
-- 			0
-- 		ELSE
-- 			1
-- 		END
-- 	) / sum(1) AS jgl
-- FROM
-- 	score
-- GROUP BY
-- 	course_id
-- ORDER BY
-- 	avg(num) ASC,
-- 	jgl DESC;
-- 
 
--
-- 20、课程平均分从高到低显示（现实任课老师）；
-- 知识点 if(ISNULL(score.num),0,(score.num))   三元运算
 
-- select score.course_id,avg(num),teacher.tname
-- from score LEFT JOIN  course on score.course_id=course.cid
-- LEFT JOIN teacher on teacher.tid=course.teacher_id
-- GROUP BY score.course_id ORDER BY avg(num)desc;
 
--
--
-- 21、查询各科成绩前三名的记录:(不考虑成绩并列情况)
-- select num from score where course_id =1 ORDER BY num desc LIMIT 0,1;
-- select num from score where course_id =1 ORDER BY num desc LIMIT 1,1;
-- select num from score where course_id =1 ORDER BY num desc LIMIT 2,1;
-- select *from
-- (
-- select student_id,course_id,num,1,
-- (select num from score as s2 where s2.course_id=s1.course_id GROUP BY s2.num ORDER BY s2.num desc LIMIT 0,1),
-- (select num from score as s2 where s2.course_id=s1.course_id GROUP BY s2.num ORDER BY s2.num desc LIMIT 3,1)as cc
--
-- from score as s1
-- )as B
-- where B.num >B.cc
-- 
 
--
-- 22、查询每门课程被选修的学生数；
-- select course_id,count(1) from score GROUP BY score.course_id
 
-- 23、查询出只选修了一门课程的全部学生的学号和姓名；
-- SELECT
-- 	A.student_id,
-- 	student.sname
-- FROM
-- 	(
-- 		SELECT
-- 			student_id,
-- 			count(1)
-- 		FROM
-- 			score
-- 		GROUP BY
-- 			student_id
-- 		HAVING
-- 			count(1) = 1
-- 	) AS A
-- LEFT JOIN student ON A.student_id = student.sid
-- 
 
--
-- 24、查询男生、女生的人数；
-- SELECT
-- 	*
-- FROM
-- 	(
-- 		SELECT
-- 			count(gender) AS F
-- 		FROM
-- 			student
-- 		WHERE
-- 			gender = "男"
-- 	) AS A,
-- 	(
-- 		SELECT
-- 			count(gender) AS M
-- 		FROM
-- 			student
-- 		WHERE
-- 			gender = "女"
-- 	) AS B
--
--
-- 25、查询姓“张”的学生名单；
-- select *from student where sname like "张%"
--
-- 26、查询同名同姓学生名单，并统计同名人数；
 
--  SELECT
--  	sname,
--  	count(sname)
--  FROM
--  	student
-- GROUP BY
--  	sname 
 
-- 27、查询每门课程的平均成绩，结果按平均成绩升序排列，平均成绩相同时，按课程号降序排列；
-- select course_id,avg(if(isnull(num),0,num))as avg from score GROUP BY course_id ORDER BY avg asc,course_id desc;
 
	--
-- 28、查询平均成绩大于85的所有学生的学号、姓名和平均成绩；
 
-- SELECT
-- 	student_id,
-- 	sname,
-- 	avg(IF(isnull(num), 0, num))
-- FROM
-- 	score
-- LEFT JOIN student ON score.student_id = student.sid
-- GROUP BY
-- 	student_id
-- 
 
--
-- 29、查询课程名称为“生物”，且分数低于60的学生姓名和分数；
-- select *from score where num<60 and course_id=(select cid from course where cname="生物")
 
-- select student.sname,score.num from score LEFT JOIN course on score.course_id=course.cid
-- LEFT JOIN student on score.student_id=student.sid where score.num <60 and course.cname="生物"
--
-- 
 
-- 30、查询课程编号为003且课程成绩在80分以上的学生的学号和姓名；
-- SELECT
-- 	A.student_id,
-- 	student.sname
-- FROM
-- 	(
-- 		SELECT
-- 			*
-- 		FROM
-- 			score
-- 		WHERE
-- 			course_id = 3
-- 		AND score.num > 80
-- 	) AS A
-- LEFT JOIN student ON A.student_id = student.sid
--
	--
-- 31、求选了课程的学生人数
-- select student_id from score GROUP BY student_id
 
	--
-- 32、查询选修“张磊”老师所授课程的学生中，成绩最高的学生姓名及其成绩；
 
-- SELECT
-- 	sname,
-- 	num
-- FROM
-- 	score
-- LEFT JOIN student ON score.student_id = student.sid
-- WHERE
-- 	score.course_id IN (
-- 		SELECT
-- 			course.cid
-- 		FROM
-- 			course
-- 		LEFT JOIN teacher ON course.teacher_id = teacher.tid
-- 		WHERE
-- 			tname = '张磊老师'
-- 	)
-- ORDER BY
-- 	num DESC
-- LIMIT 1;
 
--
	--
-- 33、查询各个课程及相应的选修人数；
-- select course.cname,count(1)from score LEFT JOIN course on score.course_id=course.cid GROUP BY course_id;
-- 
 
	--
-- 34、查询不同课程但成绩相同的学生的学号、课程号、学生成绩；
 
-- SELECT DISTINCT
-- 	s1.course_id,
-- 	s2.course_id,
-- 	s1.num,
-- 	s2.num
-- FROM
-- 	score AS s1,
-- 	score AS s2
-- WHERE
-- 	s1.num = s2.num
-- AND s1.course_id != s2.course_id;
--
--
--
	--
-- 35、查询每门课程成绩最好的前两名；
 
-- select *from
-- (
-- select student_id,course_id,num,1,
-- (select num from score as s2 where s2.course_id=s1.course_id GROUP BY s2.num ORDER BY s2.num desc LIMIT 0,1),
-- (select num from score as s2 where s2.course_id=s1.course_id GROUP BY s2.num ORDER BY s2.num desc LIMIT 2,1)as cc
--
-- from score as s1
-- )as B
-- where B.num >B.cc
-- 
 
-- 36、检索至少选修两门课程的学生学号；
 
-- SELECT
-- 	student_id,
-- 	count(1)
-- FROM
-- 	score
-- GROUP BY
-- 	student_id
-- HAVING
-- 	count(1) > 1;
 
-- 37、查询全部学生都选修的课程的课程号和课程名；
 
-- SELECT
-- 	course_id,
-- 	count(1)
-- FROM
-- 	score
-- GROUP BY
-- 	course_id
-- HAVING
-- 	count(1) = (SELECT count(1) FROM student);
 
-- 38、查询没学过“李平”老师讲授的任一门课程的学生姓名；
 
-- SELECT
-- 	*
-- FROM
-- 	student
-- WHERE
-- 	sid NOT IN (
-- 		SELECT
-- 			student_id
-- 		FROM
-- 			score
-- 		WHERE
-- 			course_id IN (
-- 				SELECT
-- 					cid
-- 				FROM
-- 					course
-- 				LEFT JOIN teacher ON course.teacher_id = teacher.tid
-- 				WHERE
-- 					teacher.tname = "李平老师"
-- 			)
-- 	)
 
-- 39、查询两门以上不及格课程的同学的学号及其平均成绩；
 
-- 先对学生进行分组 对课程数进行统计，筛选分数小于60分
-- SELECT
-- 	student_id,
-- 	count(1)
-- FROM
-- 	score
-- WHERE
-- 	num < 60
-- GROUP BY
-- 	student_id
-- HAVING
-- 	count(1) > 2;
 
-- 40、检索“004”课程分数小于60，按分数降序排列的同学学号；
 
-- 运用了排序方法，order by xx desc方法排序
--
-- SELECT
-- 	student_id
-- FROM
-- 	score
-- WHERE
-- 	course_id = 4
-- AND num < 60
-- ORDER BY
-- 	num DESC
-- 
 
-- 41、删除“002”同学的“001”课程的成绩；
 
-- 运用了表格的删除功能 delete from score表格；
-- DELETE
-- FROM
-- 	score
-- WHERE
-- 	score.course_id = 1
-- AND score.student_id = 2

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mysql基础练习题

一、表关系

二、操作表

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