Mysql學習之sql語句練習

    本文主要練習mysql中group by、having、order by、limit等的基本使用。練習題、表結構以及測試數據均借用老男孩教程中的數據。

一、表結構和數據

    表結構和表數據

/*
 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', '體育', '3'), ('4', '美術', '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', '鋼蛋'), ('3', '男', '1', '張三'), ('4', '男', '1', '張一'), ('5', '女', '1', '張二'), ('6', '男', '1', '張四'), ('7', '女', '2', '鐵錘'), ('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', '劉三'), ('14', '男', '3', '劉一'), ('15', '女', '3', '劉二'), ('16', '男', '3', '劉四');
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', '張磊老師'), ('2', '李平老師'), ('3', '劉海燕老師'), ('4', '朱雲海老師'), ('5', '李傑老師');
COMMIT;

SET FOREIGN_KEY_CHECKS = 1;

表結構和數據

    表的數據示例

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 二、練習題

    1、查詢“生物”課程比“物理”課程成績高的所有學生的學號

思路：
    獲取所有有生物課程的人（學號，成績） - 臨時表
    獲取所有有物理課程的人（學號，成績） - 臨時表
    根據【學號】連接兩個臨時表：
        學號  物理成績   生物成績



SELECT
    A.student_id,sw,tyFROM
    (SELECT student_id,num AS sw FROM score LEFT JOIN course ON score.course_id = course.cid WHERE course.cname = '生物') AS A
LEFT JOIN 
   (SELECT student_id,num AS ty FROM score LEFT JOIN course ON score.course_id = course.cid WHERE course.cname = '體育') AS B 
ON A.student_id = B.student_id
WHERE sw > IF (isnull(ty), 0, ty);

     2、查詢平均成績大於60分的同學的學號和平均成績

SELECT student_id,avg(num) FROM score GROUP BY student_id HAVING avg(num) > 60 

    3、查詢所有同學的學號、姓名、選課數、總成績

SELECT
    score.student_id,
    student.sname,
    sum(score.course_id),
    sum(score.num)
FROM
    score
LEFT JOIN student ON score.student_id = student.sid
GROUP BY
    score.student_id

    4、查詢姓“李”的老師的個數

SELECT count(*) FROM teacher WHERE tname LIKE '李%'

    5、查詢沒學過“李平”老師課的同學的學號、姓名

思路：
    先查到“李平老師”老師教的所有課ID
    獲取選過課的所有學生ID
    學生表中篩選學生id不在“獲取選過課的所有學生ID”數據



SELECT
    student.sid,
    student.sname
FROM
    student
WHERE
    student.sid NOT IN (
        SELECT DISTINCT student_id FROM score WHERE score.course_id IN (
                SELECT cid FROM course 
            LEFT JOIN teacher ON course.teacher_id = teacher.tid
                WHERE
                    teacher.tname = '李平老師'
            )
    )

    6、查詢學過“001”並且也學過編號“002”課程的同學的學號、姓名

思路：
    先查到既選擇001又選擇002課程的所有同學
    根據學生進行分組，如果學生數量等於2表示，兩門均已選擇

SELECT
    student_id,
    sname
FROM
    (SELECT * FROM score WHERE course_id = 1 OR course_id = 2) AS A
      LEFT JOIN student ON A.student_id = student.sid
         GROUP BY student_id
             HAVING count(student_id) = 2

    7、查詢學過“李平”老師所教的所有課的同學的學號、姓名

思路：
    先查李平老師教的所有課
    再查選了這些課的學生id
    根據學生id在學生表中篩選數據
    


select student_id,sname from
    (select student_id,course_id from score where course_id in 
        (SELECT cid FROM course LEFT JOIN teacher on course.teacher_id=teacher.tid WHERE teacher.tname='李平老師')) as A
LEFT JOIN student on A.student_id = student.sid

    8、查詢課程編號“002”的成績比課程編號“001”課程低的所有同學的學號、姓名

思路：
    獲取所有001課程的人（學號，成績） - 臨時表
    獲取所有002課程的人（學號，成績） - 臨時表
    根據【學號】連接兩個臨時表：
        學號  001課程成績   002課程成績

SELECT * FROM
(select student_id,num as a  from score where course_id=1) as A
LEFT JOIN 
       (select student_id,num as b from score where course_id=2) as B
 on A.student_id = B.student_id where a < if(isnull(b),0,b);

    9、查詢有課程成績小於60分的同學的學號、姓名

SELECT
    sid,
    sname
FROM student WHERE sid IN 
  (
        SELECT DISTINCT student_id FROM score WHERE num < 60
    )

    10、查詢沒有學全所有課的同學的學號、姓名

思路：
        在分數表中根據學生進行分組，獲取每一個學生選課數量
        如果數量 == 總課程數量，表示已經選擇了所有課程


SELECT
    student_id,
    sname
FROM
    score
LEFT JOIN student ON score.student_id = student.sid
GROUP BY
    student_id
HAVING
    count(course_id) = (SELECT count(1) FROM course)

    11、查詢至少有一門課與學號為“001”的同學所學相同的同學的學號和姓名

思路：
        獲取 001 同學選擇的所有課程
        獲取課程在其中的所有人以及所有課程
        根據學生篩選，獲取所有學生信息
        再與學生表連接，獲取姓名



select student_id,sname, count(course_id)
     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

    12、查詢至少學過學號為“001”同學所有課的其他同學學號和姓名

思路：
    和11類似
    先找到和001的學過的所有人
    然后個數 ＝ 001所有學科     ＝＝》 其他人可能選擇的更多


select student_id,sname, count(course_id)
   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 
          having count(course_id)=(select count(course_id) from score where student_id = 1)

    13、查詢和“002”號的同學學習的課程完全相同的其他同學學號和姓名

思路：
    類似11、12
    個數相同
    002學過的也學過


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(course_id) = (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(course_id) = (select count(1) from score where student_id = 1)

    14、刪除學習“李平”老師課的score表記錄

思路：
    查找李平老師教的課
    根據課程id刪除記錄

DELETE FROM score WHERE course_id in (
    SELECT cid from course LEFT JOIN teacher on  course.teacher_id=teacher.tid where teacher.tname='李平老師')

    15、向分數表中插入一些記錄，這些記錄要求符合以下條件：①沒有上過編號“002”課程的同學學號；②插入“002”號課程的平均成績

思路：
   insert 支持 
         inset into tb1(xx,xx) select x1,x2 from tb2;
     獲取所有沒上過002課的所有人，獲取002的平均成績數據然后進行插入


insert into score(student_id, course_id, num)
   select sid,2,(select avg(num) from score where course_id = 2)
    from student where sid not in 
       (select student_id from score where course_id = 2)