mysql復習
阿新 • • 發佈:2018-02-17
排序 max 命令 ont esc enum distinct student warn
1.數據庫操作
CREATE DATABASE 數據庫名 charset utf8; 1 查看數據庫 show databases; show create database db1; select database(); 2 選擇數據庫 USE 數據庫名 3 刪除數據庫 DROP DATABASE 數據庫名; 4 修改數據庫 alter database db1 charset utf8;
2.表操作
示例: 1. 修改存儲引擎 mysql> alter table service -> engine=innodb; 2. 添加字段 mysql>alter table student10 -> add name varchar(20) not null, -> add age int(3) not null default 22; mysql> alter table student10 -> add stu_num varchar(10) not null after name; //添加name字段之後 mysql> alter table student10 -> add sex enum(‘male‘,‘female‘) default ‘male‘ first; //添加到最前面 3. 刪除字段 mysql> alter table student10 -> drop sex; mysql> alter table service -> drop mac; 4. 修改字段類型modify mysql> alter table student10 -> modify age int(3); mysql> alter table student10 -> modify id int(11) notnull primary key auto_increment; //修改為主鍵 5. 增加約束(針對已有的主鍵增加auto_increment) mysql> alter table student10 modify id int(11) not null primary key auto_increment; ERROR 1068 (42000): Multiple primary key defined mysql> alter table student10 modify id int(11) not null auto_increment; Query OK, 0 rows affected (0.01 sec) Records: 0 Duplicates: 0 Warnings: 0 6. 對已經存在的表增加復合主鍵 mysql> alter table service2 -> add primary key(host_ip,port); 7. 增加主鍵 mysql> alter table student1 -> modify name varchar(10) not null primary key; 8. 增加主鍵和自動增長 mysql> alter table student1 -> modify id int not null primary key auto_increment; 9. 刪除主鍵 a. 刪除自增約束 mysql> alter table student10 modify id int(11) not null; b. 刪除主鍵 mysql> alter table student10 -> drop primary key;
DROP TABLE 表名;
3.數據操作
插入
1. 插入完整數據(順序插入) 語法一: INSERT INTO 表名(字段1,字段2,字段3…字段n) VALUES(值1,值2,值3…值n); 語法二: INSERT INTO 表名 VALUES (值1,值2,值3…值n); 2. 指定字段插入數據 語法: INSERT INTO 表名(字段1,字段2,字段3…) VALUES (值1,值2,值3…); 3. 插入多條記錄 語法: INSERT INTO 表名 VALUES (值1,值2,值3…值n), (值1,值2,值3…值n), (值1,值2,值3…值n); 4. 插入查詢結果 語法: INSERT INTO 表名(字段1,字段2,字段3…字段n) SELECT (字段1,字段2,字段3…字段n) FROM 表2 WHERE …;
更新
語法: UPDATE 表名 SET 字段1=值1, 字段2=值2, WHERE CONDITION; 示例: UPDATE mysql.user SET password=password(‘123’) where user=’root’ and host=’localhost’;
刪除
語法: DELETE FROM 表名 WHERE CONITION; 示例: DELETE FROM mysql.user WHERE password=’’; 練習: 更新MySQL root用戶密碼為mysql123 刪除除從本地登錄的root用戶以外的所有用戶
4.綜合練習
#1、查詢所有的課程的名稱以及對應的任課老師姓名 SELECT course.cname, teacher.tname FROM course INNER JOIN teacher ON course.teacher_id = teacher.tid; #2、查詢學生表中男女生各有多少人 SELECT gender 性別, count(1) 人數 FROM student GROUP BY gender; #3、查詢物理成績等於100的學生的姓名 SELECT student.sname FROM student WHERE sid IN ( SELECT student_id FROM score INNER JOIN course ON score.course_id = course.cid WHERE course.cname = ‘物理‘ AND score.num = 100 ); #4、查詢平均成績大於八十分的同學的姓名和平均成績 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; #5、查詢所有學生的學號,姓名,選課數,總成績(註意:對於那些沒有選修任何課程的學生也算在內) SELECT student.sid, student.sname, t1.course_num, t1.total_num FROM student LEFT JOIN ( SELECT student_id, COUNT(course_id) course_num, sum(num) total_num FROM score GROUP BY student_id ) AS t1 ON student.sid = t1.student_id; #6、 查詢姓李老師的個數 SELECT count(tid) FROM teacher WHERE tname LIKE ‘李%‘; #7、 查詢沒有報李平老師課的學生姓名(找出報名李平老師課程的學生,然後取反就可以) SELECT student.sname FROM student WHERE sid NOT IN ( SELECT DISTINCT student_id FROM score WHERE course_id IN ( SELECT course.cid FROM course INNER JOIN teacher ON course.teacher_id = teacher.tid WHERE teacher.tname = ‘李平老師‘ ) ); #8、 查詢物理課程比生物課程高的學生的學號(分別得到物理成績表與生物成績表,然後連表即可) SELECT t1.student_id FROM ( SELECT student_id, num FROM score WHERE course_id = ( SELECT cid FROM course WHERE cname = ‘物理‘ ) ) AS t1 INNER JOIN ( SELECT student_id, num FROM score WHERE course_id = ( SELECT cid FROM course WHERE cname = ‘生物‘ ) ) AS t2 ON t1.student_id = t2.student_id WHERE t1.num > t2.num; #9、 查詢沒有同時選修物理課程和體育課程的學生姓名(沒有同時選修指的是選修了一門的,思路是得到物理+體育課程的學生信息表,然後基於學生分組,統計count(課程)=1) SELECT student.sname FROM student WHERE sid IN ( SELECT student_id FROM score WHERE course_id IN ( SELECT cid FROM course WHERE cname = ‘物理‘ OR cname = ‘體育‘ ) GROUP BY student_id HAVING COUNT(course_id) = 1 ); #10、查詢掛科超過兩門(包括兩門)的學生姓名和班級(求出<60的表,然後對學生進行分組,統計課程數目>=2) SELECT student.sname, class.caption FROM student INNER JOIN ( SELECT student_id FROM score WHERE num < 60 GROUP BY student_id HAVING count(course_id) >= 2 ) AS t1 INNER JOIN class ON student.sid = t1.student_id AND student.class_id = class.cid; #11、查詢選修了所有課程的學生姓名(先從course表統計課程的總數,然後基於score表按照student_id分組,統計課程數據等於課程總數即可) SELECT student.sname FROM student WHERE sid IN ( SELECT student_id FROM score GROUP BY student_id HAVING COUNT(course_id) = (SELECT count(cid) FROM course) ); #12、查詢李平老師教的課程的所有成績記錄 SELECT * FROM score WHERE course_id IN ( SELECT cid FROM course INNER JOIN teacher ON course.teacher_id = teacher.tid WHERE teacher.tname = ‘李平老師‘ ); #13、查詢全部學生都選修了的課程號和課程名(取所有學生數,然後基於score表的課程分組,找出count(student_id)等於學生數即可) SELECT cid, cname FROM course WHERE cid IN ( SELECT course_id FROM score GROUP BY course_id HAVING COUNT(student_id) = ( SELECT COUNT(sid) FROM student ) ); #14、查詢每門課程被選修的次數 SELECT course_id, COUNT(student_id) FROM score GROUP BY course_id; #15、查詢之選修了一門課程的學生姓名和學號 SELECT sid, sname FROM student WHERE sid IN ( SELECT student_id FROM score GROUP BY student_id HAVING COUNT(course_id) = 1 ); #16、查詢所有學生考出的成績並按從高到低排序(成績去重) SELECT DISTINCT num FROM score ORDER BY num DESC; #17、查詢平均成績大於85的學生姓名和平均成績 SELECT sname, t1.avg_num FROM student INNER JOIN ( SELECT student_id, avg(num) avg_num FROM score GROUP BY student_id HAVING AVG(num) > 85 ) t1 ON student.sid = t1.student_id; #18、查詢生物成績不及格的學生姓名和對應生物分數 SELECT sname 姓名, num 生物成績 FROM score LEFT JOIN course ON score.course_id = course.cid LEFT JOIN student ON score.student_id = student.sid WHERE course.cname = ‘生物‘ AND score.num < 60; #19、查詢在所有選修了李平老師課程的學生中,這些課程(李平老師的課程,不是所有課程)平均成績最高的學生姓名 SELECT sname FROM student WHERE sid = ( SELECT student_id FROM score WHERE course_id IN ( SELECT course.cid FROM course INNER JOIN teacher ON course.teacher_id = teacher.tid WHERE teacher.tname = ‘李平老師‘ ) GROUP BY student_id ORDER BY AVG(num) DESC LIMIT 1 ); #20、查詢每門課程成績最好的前兩名學生姓名 #查看每門課程按照分數排序的信息,為下列查找正確與否提供依據 SELECT * FROM score ORDER BY course_id, num DESC; #表1:求出每門課程的課程course_id,與最高分數first_num SELECT course_id, max(num) first_num FROM score GROUP BY course_id; #表2:去掉最高分,再按照課程分組,取得的最高分,就是第二高的分數second_num SELECT score.course_id, max(num) second_num FROM score INNER JOIN ( SELECT course_id, max(num) first_num FROM score GROUP BY course_id ) AS t ON score.course_id = t.course_id WHERE score.num < t.first_num GROUP BY course_id; #將表1和表2聯合到一起,得到一張表t3,包含課程course_id與該們課程的first_num與second_num SELECT t1.course_id, t1.first_num, t2.second_num FROM ( SELECT course_id, max(num) first_num FROM score GROUP BY course_id ) AS t1 INNER JOIN ( SELECT score.course_id, max(num) second_num FROM score INNER JOIN ( SELECT course_id, max(num) first_num FROM score GROUP BY course_id ) AS t ON score.course_id = t.course_id WHERE score.num < t.first_num GROUP BY course_id ) AS t2 ON t1.course_id = t2.course_id; #查詢前兩名的學生(有可能出現並列第一或者並列第二的情況) SELECT score.student_id, t3.course_id, t3.first_num, t3.second_num FROM score INNER JOIN ( SELECT t1.course_id, t1.first_num, t2.second_num FROM ( SELECT course_id, max(num) first_num FROM score GROUP BY course_id ) AS t1 INNER JOIN ( SELECT score.course_id, max(num) second_num FROM score INNER JOIN ( SELECT course_id, max(num) first_num FROM score GROUP BY course_id ) AS t ON score.course_id = t.course_id WHERE score.num < t.first_num GROUP BY course_id ) AS t2 ON t1.course_id = t2.course_id ) AS t3 ON score.course_id = t3.course_id WHERE score.num >= t3.second_num AND score.num <= t3.first_num; #排序後可以看的明顯點 SELECT score.student_id, t3.course_id, t3.first_num, t3.second_num FROM score INNER JOIN ( SELECT t1.course_id, t1.first_num, t2.second_num FROM ( SELECT course_id, max(num) first_num FROM score GROUP BY course_id ) AS t1 INNER JOIN ( SELECT score.course_id, max(num) second_num FROM score INNER JOIN ( SELECT course_id, max(num) first_num FROM score GROUP BY course_id ) AS t ON score.course_id = t.course_id WHERE score.num < t.first_num GROUP BY course_id ) AS t2 ON t1.course_id = t2.course_id ) AS t3 ON score.course_id = t3.course_id WHERE score.num >= t3.second_num AND score.num <= t3.first_num ORDER BY course_id; #可以用以下命令驗證上述查詢的正確性 SELECT * FROM score ORDER BY course_id, num DESC;
更多:http://www.cnblogs.com/wupeiqi/articles/5748496.html
mysql復習