5 多表查询之练习题（重在思路）
表准备
/* 数据导入： 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;
1、查询所有的课程的名称以及对应的任课老师姓名
# 写多表查询题跟写代码是一样的 先写思路再写sql # 不要想着一次性写完 写一点查一点再写一点 -- 1、查询所有的课程的名称以及对应的任课老师姓名 # 1.先明确需要用到几张表 老师表与课程表 # 2.查询的结果也必须来源于两种表 # 步骤1 先连表 -- SELECT -- course.cname, -- teacher.tname -- FROM -- course -- INNER JOIN teacher ON course.teacher_id = teacher.tid;
2.查询平均成绩大于八十分的同学的姓名和平均成绩
# 先明确需要用到两张表 # 1.查询平均成绩大于80分的学生id号 # 按照学生id分组 之后求每个学生的平均成绩 -- select student_id,avg(num) from score group by student_id; # 在使用having过滤出平均成绩大于80分的数据 -- select student_id,avg(num) as avg_num from score group by student_id -- HAVING avg(num) > 80 -- ; # 将上述的表与学生表按照学生id拼接到一起 SELECT student.sname, t1.avg_num FROM student INNER JOIN ( SELECT student_id, avg( num ) AS avg_num FROM score GROUP BY student_id HAVING avg( num ) > 80 ) AS t1 ON student.sid = t1.student_id;
3.、查询没有报李平老师课的学生姓名
SELECT
sname
FROM
student
WHERE
sid NOT IN (
SELECT DISTINCT
student_id
FROM
score
WHERE
course_id IN (
SELECT
cid
FROM
course
WHERE
teacher_id = ( SELECT tid FROM teacher WHERE tname = '李平老师' )));
4、 查询没有同时选修物理课程和体育课程的学生姓名(只要报了物理或者体育的 两门都报、都不报的都不要)
# 步骤1 先查询物理课程和体育课程的id号
-- select cid from course where cname in ('物理','体育');
# 步骤2 再根据课程id号去分数表中筛选出所有跟该课程id号相关的数据
-- select * from score where course_id in (select cid from course where cname in ('物理','体育')); -- 选了两门的 选了一门的
# 步骤3 从上述结果集中移除选了两门及以上(按照学生id分组 统计每个学生选的门数)
-- select student_id from score where course_id in (select cid from course where cname in ('物理','体育')) group by score.student_id having count(course_id) = 1;
# 步骤4 根据学生id去学生表中筛选出对应的学生姓名
-- SELECT
-- sname
-- FROM
-- student
-- WHERE
-- sid IN (
-- SELECT
-- student_id
-- FROM
-- score
-- WHERE
-- course_id IN (
-- SELECT
-- cid
-- FROM
-- course
-- WHERE
-- cname IN ( '物理', '体育' ))
-- GROUP BY
-- score.student_id
-- HAVING
-- count( course_id ) = 1
-- );
5、 查询挂科超过两门(包括两门)的学生姓名和班级
# 步骤1 先查询所有分数小于60的数据
-- select * from score where num < 60;
# 步骤2 按照学生id分组 筛选出数据项大于等于2的数据
-- select student_id from score where num < 60 group by student_id having count(course_id) >= 2;
# 步骤3 由于最后所需的数据来源于两张表 所以可以先提前连表
SELECT
sname,
caption
FROM
student
INNER JOIN class ON student.class_id = class.cid
WHERE
student.sid IN ( SELECT student_id FROM score WHERE num < 60 GROUP BY student_id HAVING count( course_id ) >= 2 );
