sql语句练习题及答案

表结构

创建表数据
    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;

临时表,链表查询
    -- 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 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;

    -- 查询所有同学的学号、姓名、选课数、总成绩
    SELECT A.student_id,student.sname,A.choice_num,A.sum_score from (
    SELECT student_id,COUNT(1) as choice_num ,SUM(num) as sum_score from score GROUP BY student_id) as A
    LEFT JOIN
    student on A.student_id=student.sid
    
    -- 查询课程编号“2”的成绩比课程编号“1”课程低的所有同学的学号、姓名
    SELECT student.sid,student.sname from student where student.sid in (
    SELECT A.student_id from (
    (SELECT student_id,num from score LEFT JOIN course on score.course_id=course.cid where cid='2')A
    LEFT JOIN
    (SELECT student_id,num from score LEFT JOIN course on score.course_id=course.cid where cid='1')B
    on A.student_id=B.student_id) WHERE A.num>B.num);
    
    -- 查询和“2”号的同学学习的课程完全相同的其他同学学号和姓名

    SELECT student_id from (
    SELECT * from score where student_id=(
    SELECT student_id from score GROUP BY student_id HAVING count(1)=(
    SELECT count(1) as count_course from score GROUP BY student_id HAVING student_id=2 )and student_id!=2 ) and  course_id in
    (select course_id from score WHERE student_id=2)) as A GROUP BY student_id HAVING count(*)=
    (SELECT count(1) as count_course from score GROUP BY student_id HAVING student_id=2)
    
    -- 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,avg(num) as avgnum,student.sname from score  LEFT JOIN student on score.student_id=student.sid
    GROUP BY student_id HAVING avgnum > 85

    -- 查询课程名称为“物理”，且分数低于60的学生姓名和分数；
    SELECT student.sname,score.num from course LEFT JOIN score on score.course_id=course.cid LEFT JOIN student on score.student_id=student.sid
    WHERE course.cname='物理' and score.num < 60
    
    -- 查询课程编号为3且课程成绩在80分以上的学生的学号和姓名；
    SELECT student_id,student.sname from course LEFT JOIN score on score.course_id=course.cid LEFT JOIN student on score.student_id=student.sid
    WHERE cid=3 and score.num>80
    
    -- 查询选修“李平老师'所授课程的学生中，成绩最高的学生姓名及其成绩；
    SELECT A.num,A.sname,A.cname from (
    SELECT score.num,student.sname,course.cname from teacher LEFT JOIN course on course.teacher_id=teacher.tid LEFT JOIN score on course.cid=score.course_id
    LEFT JOIN student on score.student_id=student.sid
    WHERE teacher.tname='李平老师' ORDER BY num desc ) as A GROUP BY cname
    
    -- 求选了课程的学生人数
    SELECT count(*) as person from (
    SELECT student.sid from student LEFT JOIN score as score1 on score1.student_id=student.sid  WHERE student.sid  in (SELECT student_id from score GROUP BY student_id)
    GROUP BY student.sid ) as A
    
    -- 查询没学过“李平老师”讲授的任一门课程的学生姓名；
    SELECT student_id,sname from score LEFT JOIN student
    on score.student_id=student.sid
    WHERE score.student_id not in (
    SELECT DISTINCT s1.student_id from teacher LEFT JOIN course on course.teacher_id=teacher.tid
    LEFT JOIN score  as s1 on course.cid=s1.course_id
    WHERE tname='李平老师'  )
        
    

条件查询语句    
    -- 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 student.sid not in (
    SELECT student_id from
    (SELECT cid from course LEFT JOIN teacher on course.teacher_id=teacher.tid
    where tname='李平老师' )as A LEFT JOIN score on score.course_id=A.cid GROUP BY student_id)
    
    -- 查询学过“李平老师”所教的所有课的同学的学号、姓名
    SELECT student.sid,student.sname from student where student.sid in (
    SELECT student_id from
    (SELECT cid from course LEFT JOIN teacher on course.teacher_id=teacher.tid
    where tname='李平老师' )as A LEFT JOIN score on score.course_id=A.cid GROUP BY student_id)
    
    -- 查询至少有一门课与学号为“1”的同学所学相同的同学的学号和姓名
    SELECT student.sid,student.sname from student where sid in (
    SELECT student_id from score where course_id in (
    SELECT course_id from score where student_id = '1') GROUP BY student_id HAVING count(course_id)>1);
    
    -- 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 s1.student_id,s1.course_id,s1.num from score as s1,score as s2 WHERE s1.num=s2.num and s1.student_id=s2.student_id and  s1.course_id!=s2.course_id      

分组查询
    -- 查询平均成绩大于60分的同学的学号和平均成绩
    SELECT student_id,AVG(num) as number from score GROUP BY student_id HAVING number > 60;
    
    -- 查询学过“1”并且也学过编号“2”课程的同学的学号、姓名；
    SELECT student_id,count(1) as count_course from score where course_id in (1,2) GROUP BY student_id HAVING count_course>1;
    
    -- 查询有课程成绩小于60分的同学的学号、姓名
    SELECT sid,sname from student where sid in (
    SELECT student_id from score WHERE num < 60 GROUP BY student_id)
    
    -- 查询没有学全所有课的同学的学号、姓名
    SELECT student.sid,student.sname from student where student.sid in (
    SELECT student_id from score GROUP BY student_id HAVING count(course_id) < (
    SELECT count(1) from course));
    
    -- 查询至少有一门课与学号为“1”的同学所学相同的同学的学号和姓名
    SELECT student.sid,student.sname from student where sid in (
    SELECT student_id from score where course_id in (
    SELECT course_id from score where student_id = '1') GROUP BY student_id HAVING count(course_id)>1) and sid !=1;
    
    -- 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) as 最高分,min(num) as 最低分 from score GROUP BY course_id;
    
    -- 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) as 最高分,min(num) as 最低分 from score GROUP BY course_id;
    
    -- 课程平均分从高到低显示（现实任课老师）
    SELECT course_id,teacher_id,AVG(num) as avgnum from course LEFT JOIN score
    on score.course_id=course.cid
    GROUP BY course_id ORDER BY avgnum desc
    
    -- 查询每门课程被选修的学生数
    SELECT course_id,count(*) as person from score GROUP BY course_id
    
    -- 查询出只选修了一门课程的全部学生的学号和姓名
    SELECT * from (
    SELECT student_id,course_id,count(*) as course_count from score GROUP BY student_id ) as  A
    LEFT JOIN student on student.sid=A.student_id   WHERE A.course_count=1
    
    -- 查询男生、女生的人数；
    select gender,count(*) as person from student GROUP BY gender
    
    -- 查询同名同姓学生名单，并统计同名人数
    SELECT sname,count(*) as person from student GROUP BY student.sname HAVING person>1
    
    -- 检索至少选修两门课程的学生学号；
    SELECT student_id,count(*) as count_course from score GROUP BY student_id HAVING count_course >= 2
    
    -- 查询全部学生都选修的课程的课程号和课程名；
    select course_id,count(*) as person from score GROUP BY course_id HAVING person=(SELECT count(1) from student)
        
    -- 查询学的课程最少的学生学号和课程号
    SELECT s1.student_id,s1.course_id from score as s1
    GROUP BY s1.student_id ORDER BY count(1) limit 1
    
    -- 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,course_id,avg(num) from score where num < 60 GROUP BY student_id HAVING count(1) >= 2
    
    -- 检索“4”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 course_id=4 and num < 60 ORDER BY num desc

        
模糊匹配
    -- 查询姓“李”的老师的个数
    select * from teacher where tname like '李%'
        
    -- 查询姓“张”的学生名单；
    SELECT * from student WHERE sname like '张%';
    
    
排序
    -- 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
    select course_id, avg(num) as avgnum,sum(case when score.num > 60 then 1 else 0 END)/count(1)*100 as percent from score group by course_id order by avgnum asc,percent desc;
    
    -- 查询各科成绩前三名的记录:(不考虑成绩并列情况)
    SELECT score1.sid,score1.course_id,res.first_num,res.second_num,res.third_num from score as score1 LEFT JOIN (
    SELECT sid,
    (SELECT num from score as score2 WHERE score2.course_id=score3.course_id ORDER BY num desc LIMIT 0,1) as first_num,
    (SELECT num from score as score2 WHERE score2.course_id=score3.course_id ORDER BY num desc LIMIT 3,1) as second_num,
    (SELECT num from score as score2 WHERE score2.course_id=score3.course_id ORDER BY num desc LIMIT 4,1) as third_num
    from score as score3
    ) as res
    on score1.sid=res.sid GROUP BY score1.course_id;
    
    -- 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 * from (
    SELECT course_id,avg(num) as avgnum from score GROUP BY course_id ) as A ORDER BY A.avgnum asc,A.course_id DESC
    
    -- 查询每门课程成绩最好的前两名；
    select score1.course_id ,res.first_num,res.second_num from score as score1 LEFT JOIN  
    ( select sid,
    (select num from score as score2 WHERE score3.course_id=score2.course_id ORDER BY score2.num desc LIMIT 0,1) as first_num,
    (select num from score as score2 WHERE score3.course_id=score2.course_id ORDER BY score2.num desc LIMIT 3,1) as second_num
    from score as score3
    ) as res  
    on res.sid=score1.sid
    GROUP BY score1.course_id
    

case when then else end
    -- 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
    select course_id, avg(num) as avgnum,sum(case when score.num > 60 then 1 else 0 END)/count(1)*100 as percent from score group by course_id order by avgnum asc,percent desc;

delete
    -- 删除“2”同学的“1”课程的成绩；
    delete from score where student_id=2 and course_id=1