mysql 练习题
导出现有数据库数据：
- C:\Users\Administrator>mysqldump -u root db1>D:\agon\db1.sql -p #结构+数据
- mysqldump -u用户名 -d 数据库名称 >导出文件路径 -p #结构
导入现有数据库：
- mysqldump -u root 数据库名称 < 文件路径 -p #箭头是重点
/* Navicat Premium Data Transfer Source Server : localhost Source Server Type : MySQL Source Server Version : 50624 Source Host : localhost Source Database : sqlexam Target Server Type : MySQL Target Server Version : 50624 File Encoding : utf-8 Date: 10/21/2016 06:46:46 AM */ SET NAMES utf8; 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` -- ---------------------------- BEGIN; INSERT INTO `class` VALUES ('1', '三年二班'), ('2', '三年三班'), ('3', '一年二班'), ('4', '二年九班'); COMMIT; -- ---------------------------- -- 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` -- ---------------------------- BEGIN; INSERT INTO `course` VALUES ('1', '生物', '1'), ('2', '物理', '2'), ('3', '体育', '3'), ('4', '美术', '2'); COMMIT; -- ---------------------------- -- 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` -- ---------------------------- BEGIN; INSERT INTO `score` VALUES ('1', '1', '1', '10'), ('2', '1', '2', '9'), ('5', '1', '4', '66'), ('6', '2', '1', '8'), ('8', '2', '3', '68'), ('9', '2', '4', '99'), ('10', '3', '1', '77'), ('11', '3', '2', '66'), ('12', '3', '3', '87'), ('13', '3', '4', '99'), ('14', '4', '1', '79'), ('15', '4', '2', '11'), ('16', '4', '3', '67'), ('17', '4', '4', '100'), ('18', '5', '1', '79'), ('19', '5', '2', '11'), ('20', '5', '3', '67'), ('21', '5', '4', '100'), ('22', '6', '1', '9'), ('23', '6', '2', '100'), ('24', '6', '3', '67'), ('25', '6', '4', '100'), ('26', '7', '1', '9'), ('27', '7', '2', '100'), ('28', '7', '3', '67'), ('29', '7', '4', '88'), ('30', '8', '1', '9'), ('31', '8', '2', '100'), ('32', '8', '3', '67'), ('33', '8', '4', '88'), ('34', '9', '1', '91'), ('35', '9', '2', '88'), ('36', '9', '3', '67'), ('37', '9', '4', '22'), ('38', '10', '1', '90'), ('39', '10', '2', '77'), ('40', '10', '3', '43'), ('41', '10', '4', '87'), ('42', '11', '1', '90'), ('43', '11', '2', '77'), ('44', '11', '3', '43'), ('45', '11', '4', '87'), ('46', '12', '1', '90'), ('47', '12', '2', '77'), ('48', '12', '3', '43'), ('49', '12', '4', '87'), ('52', '13', '3', '87'); COMMIT; -- ---------------------------- -- 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` -- ---------------------------- BEGIN; INSERT INTO `student` VALUES ('1', '男', '1', '理解'), ('2', '女', '1', '钢蛋'), ('3', '男', '1', '张三'), ('4', '男', '1', '张一'), ('5', '女', '1', '张二'), ('6', '男', '1', '张四'), ('7', '女', '2', '铁锤'), ('8', '男', '2', '李三'), ('9', '男', '2', '李一'), ('10', '女', '2', '李二'), ('11', '男', '2', '李四'), ('12', '女', '3', '如花'), ('13', '男', '3', '刘三'), ('14', '男', '3', '刘一'), ('15', '女', '3', '刘二'), ('16', '男', '3', '刘四'); COMMIT; -- ---------------------------- -- 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=6 DEFAULT CHARSET=utf8; -- ---------------------------- -- Records of `teacher` -- ---------------------------- BEGIN; INSERT INTO `teacher` VALUES ('1', '张磊老师'), ('2', '李平老师'), ('3', '刘海燕老师'), ('4', '朱云海老师'), ('5', '李杰老师'); COMMIT; SET FOREIGN_KEY_CHECKS = 1;
C:\Users\Administrator>mysqldump -u root db1>D:\agon\db1.sql -p 转储命令 select * from course; SELECT teacher_id,count(cname) from course group by teacher_id; select * from course left join teacher on course.teacher_id=teacher.tid; SELECT * from student left join class on student.class_id=class.cid; 2、查询“生物”课程比“物理”课程成绩高的所有学生的学号； 思路：获取所有生物课程的人(学号,成绩)-临时表 获取所有生物课程的人(学号,成绩)-临时表 根据 学号 连接两个临时表： 学号 物理成绩 生物成绩 然后在进行筛选 select A.student_id from (select student_id,num from score LEFT JOIN course on score.course_id=course.cid WHERE cname='生物') as A left join (select student_id,num from score LEFT JOIN course on score.course_id=course.cid WHERE 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.avv from (SELECT student_id,avg(num) as avv 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；student.sid,count(student.sid) select student_id,count(student_id),sum(num),student.sname from score left join student on score.student_id=student.sid group by student_id; 5、查询姓“李”的老师的个数； select count(tname) from teacher where tname like'李%'; 6、查询没学过“叶平”老师课的同学的学号、姓名； 获取李平老师课程ID select cid from course left join teacher on course.teacher_id=teacher.tid where tname='李平老师'; 查询所有学过老师课的学生的id, select student_id from score where course_id in (2,4) group by student_id; select * from tb12 where id in (select id from tb11) 这个是格式 select student.sid,student.sname from student where sid not in (select student_id from (select student_id from score where course_id in (select cid from course left join teacher on course.teacher_id=teacher.tid where tname='李平老师') group by student_id)as B ); 7、查询学过“001”并且也学过编号“002”课程的同学的学号、姓名； 找到所有选了001课程的同学的id和所有选了002课程的同学的id select student_id,sname from (select student_id,course_id from score where course_id=1 or course_id=2)as B left join student on B.student_id=student.sid GROUP BY student_id HAVING count(student_id>1); 不加having也行 8、查询学过“叶平”老师所教的所有课的同学的学号、姓名； 先找李平老师教过的课的id select cid from course LEFT JOIN teacher on course.teacher_id=teacher.tid where tname like '李平%'; 通过cid找到对应的sid select student_id,sname from student INNER JOIN (SELECT student_id from score where course_id in (select cid from course LEFT JOIN teacher on course.teacher_id=teacher.tid where tname like '李平%'))as B on B.student_id=student.sid GROUP BY student_id HAVING COUNT(student_id)>1; 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； 先找到002课程的所有成绩和student_id在找到001的num和student_id select student_id,course_id,num from score where course_id=2; select student_id,course_id,num from score where course_id=1; 这里有个坑，我操操操，第57行如果有A.num和B.num的话会报重复列的错， 所以够用就行，不要多谢闲的蛋疼 SELECT student.sid,student.sname from ( select * from (select student_id,course_id,num from score where course_id=2)as A INNER JOIN (select student_id,course_id,num from score where course_id=1)as B on A.student_id=B.student_id where A.num<B.num )as C INNER JOIN student on C.student_id=student.sid; 10、查询有课程成绩小于60分的同学的学号、姓名； SELECT student.sid,sname,num FROM score INNER JOIN student on score.student_id=student.sid where num<60; 11、查询没有学全所有课的同学的学号、姓名； SELECT A.student_id,count(A.student_id),sname from (SELECT student_id,course_id from score)as A LEFT JOIN student on A.student_id=student.sid group by A.student_id HAVING count(A.student_id)<(select count(1) 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； 先找到学好为001的学生的课程ID 124 限制死了，就算你有三门也是124里面的三门，注意一下 select sid,sname from (SELECT student_id,course_id from score where student_id!=1 and course_id in (1,2,4))as A LEFT JOIN student on A.student_id=student.sid GROUP BY sid; 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； 也是限制死了，从select * from score WHERE course_id in (1,2,4) 分组后计数最多为3 但是可能人家是选了四门课，这是注意点 SELECT student.sid,student.sname from student INNER JOIN ( 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) )as A on student.sid=A.student_id; 14、查询和“001”号的同学学习的课程完全相同的其他同学学号和姓名； 先找到和001一样都学过3门的学生id 在通过course_id将表约束为只有1,2,4三门的学生成绩表，通过这个表分组筛选出个数为3的student_id明显没有符合条件的 select student_id from score where student_id in (select student_id from score where student_id!=1 GROUP BY student_id having count(course_id)=3) and course_id in(1,2,4) GROUP BY student_id having count(1)=3; select student_id from score 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“叶平”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 tname='李平老师' ); 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； 用到insert into 表名(a,b,c) select a,b,c from 表名 // 如果bc不是表的列明则bc必须是单值 先找到选了002课程的所有同学的id 主要是讲新的插入姿势 insert into score(student_id,course_id,num) 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； 知识点把列的内容横着放，涉及到子查询，每个学生ID对应三门成绩，还需把所有的null设置为0 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=3)as 数学, (select num from score as s2 where s2.student_id=s1.student_id and course_id=4)as 英语, avg(if(isnull(s1.num),0,s1.num)), avg(num) from score as s1 GROUP BY student_id ORDER BY avg(if(isnull(s1.num),0,s1.num)) desc; 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； 知识点：select case when num<60 then 0 else num end from score; case when..THEN..ELSE..END 可直接用于查 大于60分的=1，小于60分的=0，二者求和后就是及格人数，用及格人数/选该科目的总人数 就是及格率 select course_id,avg(num), sum(case when score.num>60 then 1 else 0 end)/count(1)*100 as percent from score GROUP BY course_id ORDER BY avg(num) asc,percent desc; 20、课程平均分从高到低显示（现实任课老师）； 知识点：avg(if(isnull(score.num),0,score.num)) 如果为null则为0否则为null.num select course_id,teacher.tname,avg(if(isnull(score.num),0,score.num)) from score LEFT JOIN course on score.course_id=course.cid LEFT JOIN teacher on course.teacher_id=teacher.tid GROUP BY course_id ORDER BY avg(if(isnull(score.num),0,score.num)) desc; 21、查询各科成绩前三名的记录:(不考虑成绩并列情况) 考虑成绩并列的话，应该先按成绩分组，这样如果有3个100分则他们都是第一名 select course_id, (select num from score as s1 WHERE s1.course_id=s2.course_id GROUP BY num ORDER BY num desc LIMIT 0,1)as A, (select num from score as s1 WHERE s1.course_id=s2.course_id GROUP BY num ORDER BY num desc LIMIT 1,1)as B, (select num from score as s1 WHERE s1.course_id=s2.course_id GROUP BY num ORDER BY num desc LIMIT 2,1)as C from score as s2 GROUP BY course_id; 22、查询每门课程被选修的学生数； select course_id,count(1) from score GROUP BY 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 student_id,student.sname from score LEFT JOIN student on score.student_id=student.sid GROUP BY student_id HAVING COUNT(course_id)=1 24、查询男生、女生的人数； select gender,COUNT(1) from student GROUP BY gender; 25、查询姓“张”的学生名单； SELECT sname 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(1) from student GROUP BY sname HAVING count(1)>1; 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)) from score GROUP BY course_id ORDER BY avg(if(isnull(num),0,num)) 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 HAVING avg(if(isnull(num),0,num))>85 29、查询课程名称为“数学”，且分数低于60的学生姓名和分数； select student.sid,sname from score LEFT JOIN course on score.course_id=course.cid LEFT JOIN student on score.student_id=student.sid where cname='生物' and num<60 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 student_id,sname from score LEFT JOIN student on score.student_id=student.sid where course_id=3 and num>80 31、求选了课程的学生人数 select count(distinct student_id) from score; select count(1) from (select student_id from score GROUP BY student_id) as A; 32、查询选修“杨艳”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 course on score.course_id=course.cid LEFT JOIN student on score.student_id=student.sid 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 course.cid=score.course_id 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 * from teacher as s1,teacher as s2; 5*5=25 笛卡尔机原理 select s1.student_id,s1.course_id,s1.num from score as s1,score as s2 where s1.sid!=s2.sid and s1.course_id!=s2.course_id and s1.num=s2.num; 35、查询每门课程成绩最好的前两名； SELECT course_id, (select num from score as s1 where s1.course_id=s2.course_id GROUP BY num ORDER BY num desc LIMIT 0,1)as A, (select num from score as s1 where s1.course_id=s2.course_id GROUP BY num ORDER BY num desc LIMIT 1,1)as B from score as s2 GROUP BY course_id; 36、检索至少选修两门课程的学生学号； SELECT student_id from score GROUP BY student_id HAVING count(course_id)>1; 37、查询全部学生都选修的课程的课程号和课程名； 把score以课程号分组加个条件：count(1)=student表中的行数===》这样拿到课程id，连表course拿到课程名 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“叶平”老师讲授的任一门课程的学生姓名； 先找到李平老师教过的所有课的学生的id SELECT sid,sname 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 tname='李平老师') GROUP BY student_id ); 39、查询两门以上不及格课程的同学的学号及其平均成绩； select student_id,count(1),avg(if(ISNULL(num),0,num)) 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； select student_id FROM score WHERE num<60 and course_id = 4 ORDER BY num desc; 41、删除“002”同学的“001”课程的成绩； DELETE from score where student_id=2 and course_id=1;
mysql总结
# SQL 语句的格式 SELECT DISTINCT <select_list> FROM <left_table> <join_type> JOIN <right_table> ON <join_condition> WHERE <where_condition> GROUP BY <group_by_list> HAVING <having_condition> ORDER BY <order_by_condition> LIMIT <limit_number> # SQL 语句的执行顺序 (1) FROM <left_table> (2) ON <join_condition> (3) <join_type> JOIN <right_table> (4) WHERE <where_condition> (5) GROUP BY <group_by_list> (6) HAVING <having_condition> (7) SELECT (8) DISTINCT <select_list> (9) ORDER BY <order_by_condition> (10) LIMIT <limit_number>
