MySQL中的創建庫、表以及查詢語句對我們以後很好的應用數據庫是很大有幫助的,博文中是對這些基礎語句的總結,希望會對大家有些幫助
1、創建與刪除數據庫
創建數據庫 mysql> create database testdb; mysql> create database if not exists testdb; mysql> create schema if not exists student character set 'gbk' collate 'gbk_chinese_ci'; 刪除數據庫 mysql> drop database testdb;
2、創建與刪除表
- CREATE TABLE [if not exists] tb_name(col_name,col_definstion,constraint)
- 創建表
- mysql> create table tb (id int unsigned not null auto_increment primary key,Name char(20)
- not null,Age tinyint not null);
- mysql> create table tb (id int unsigned not null auto_increment,Name char(20) not null,Age
- tinyint not null,primary key(id));
- mysql> create database mydb;
- mysql> use mydb;
- mysql> create table students(name char(20) not null,age tinyint unsigned,gender char(1)
- not null);
- mysql> create table courses(ID tinyint unsigned not null auto_increment primary key,Couse
- varchar(50) not null);
- mysql> create table courses(name char(20) not null,age tinyint unsigned,gender char(1)
- not null); ---從一張表中查出需要的數並創建爲一個新表,但是很多字段的屬性沒有存在,需要自己在重新定義
- mysql> create table testcourses select * from courses where CID <=2;
- 以其它表爲模板,創建一個新表,字段的屬性還會存在
- mysql> create table test like courses;
- 刪除表:DROP TABLE tb_name;
- mysql> drop table testcourses;
3、修改表
- ALTER TABLE tb_name;
- mysql>alter table students change course Course varchar(100) after name;
- mysql>alter table students add course varchar(100);
- 向表中插入數據
- insert into tb_name (col,col2,....) values (val1,val2,....);
- insert into tutors (Tname,Gender,Age) values ('jerry','M',24); -----批量插入方式
- insert into tutors set Tname='Tom',Genser='F',Age=30; -----只能實現單個字段插入
- insert into tutors (Tname,Gender,Age) select Name,Genser,Age from students where Age >=20
- select * from tutors order by TID desc limit 1; -----查看降序的第一行
- select last_insert_ID(); -----查詢插入的最後一個序列號
- 更改數據庫
- UPDATE tb_name SET column=value where
- mysql>update students set Course='wg' where Name='j'; -----更改j的課程爲wg
- 刪除表中的某一字段
- DELETE FROM students WHERE Course='';
- mysql>delete from students where Course='wg';
4、創建用戶
CREATE USER 'USERNAME'@'HOST' IDENTIFIED BY 'PASSWORD'; mysql> create user 'jerry'@'%' identified by 'jerry'; ------創建用戶 修改用戶密碼的方法 1) mysql> SET PASSWORD FOR 'USERNAME'@'HOST'=PASSWORD('NEW_PASSWORD'); 2) mysqladmin -uUSERNAME -hHOST -p password 'password' ------不進入mysql修改密碼 mysqladmin -uroot -h127.0.0.1 -p passwd'123456' 3) mysql> UPDATE user SET Password=PASSWORD('password') WHERE USER='root' AND Host='127.0.0.1'; UPDATE user SET Password=PASSWORD('123456') WHERE USER='root' AND Host='127.0.0.1'; 給用戶授權 GRANT pri1,pri2,......ON DB_NAME.TB_NAME TO 'USERNAME'@'HOST' [IDENTIFIED BY 'password'] mysql> grant all privileges on test.* to 'jerry'@'%'; -----給用戶所有權限 REVOKE pri1,pri2,.....ON DB_NAME.TB_NAME FROM 'USERNAME'@'HOST'
5、關於show命令
SHOW GRANTS FOR 'USERNAME'@'HOST' -----查看用戶的授權 mysql> show databases; -----查看數據庫 mysql> desc students; -----查看一張表的結夠 mysql> show grants for 'jerry'@'%'; -----查看創建用戶的信息 mysql> show character set; -----查看當前服務器所支持的字符集 mysql> show collation; -----查看排序規則 mysql> show engines; -----查看數據庫中的所有引擎 mysql> show table status like 'user'; -----查看一張表的狀態信息(橫向顯示的) mysql> show table status like 'user'\G: -----查看一張表的狀態信息(縱向顯示)
6、select語句練習
下面的語句查詢操作所使用的數據庫已經上添加到附件
- 簡單語句查詢
- select * from students; ------顯示錶中的所有內容
- select Name,Age from students; ------顯示students表中的Name和Age列
- select distict Gender from students; ------相同的內容只顯示一次
- 選擇students表中年齡大於20的同學(以下三種方式):
- select * from students where Age>=20;
- select Name,Age from students where Age>=20;
- select Name,Age from students where Age+1>20;
- 查找年齡大於20的同學並且按降序排列:
- select Name,Age from students where Age>20 order by Age desc;
- 年齡大於等於20並且是男性的同學:
- select Name from students where Age>20 and Gender='M';
- 年齡不大於20的同學:
- select Name,Age,Gender from students where not Age>20;
- 小於等於20的女同學:
- select Name,Age,Gender from students where not (Age>20 or Gender=‘M’);
- 年齡在(21-24)之間的同學(以下兩種方式):
- select Name,Age from students where Age>20 and Age<25;
- select Name,Age from students where Age between 20 and 25;
- 顯示以Y開頭的名稱(這裏限定了姓名的長度)("_"表示任意單個字符):
- select Name from students where Name like 'Y___';
- 顯示以Y開頭的姓名:
- select Name from students where Name like 'Y%';
- 名稱中含有ing的名稱(“%”表示任意長度的任意字符):
- select Name from students where Name like '%ing%';
- 顯示以M或N或Y開頭的名字(支持正則表達式):
- select Name from students where Name rlike '^[MNY].*$';
- 顯示年齡是18、20、25的同學:
- select Name from students where Age IN (18,20,25);
- 顯示挑選課程號(CID1)爲空的同學:
- select Name from students where CID1 is null;
- 把查詢後的結果進行降序排序(ASC升序,desc降序)
- select Name,CID1 from students where CID1 is not null order by CID1 desc;
- select Name AS Student_Name from students;顯示查詢的Name表頭名變爲name
- 隔兩行數據向後取三行數據:
- select Name from students limit 2,3;
- 所有同學的平均年齡:
- select AVG(age) from students;
- 顯示年齡最大的同學:
- select MAX(age) from students;
- 顯示年齡最小的同學:
- select MIN(age) from students;
- 顯示所有同學的年齡總和:
- select SUM(age) from students;
- 顯示所有同學的個數:
- select count(age) from students;
- 顯示所有男同學的平均年齡:
- select AVG(age) from students where Gender=’M‘;
- 顯示所有女同學的平均年齡:
- select AVG(age) from students where Gender=’F‘;
- 顯示男女同學的平均年齡:
- select Gender,avg(age) from students group by Gender;
- 顯示選修CID1的同學
- select count(CID1) AS Persons,CID1 from students group by CID1;
- 顯示選修人數大於2的課程:
- select count(CID1) AS Persons,CID1 from students group by CID1 having Persons>=2;
- 多表查詢
- 每位同學及其他所學習的課程名稱(以下四種方式)
- select students.Name,courses.Cname from students,courses where students.CID1=courses.CID;
- select s.Name,c.Cname from students AS s,courses AS c where s.CID1=c.CID;
- select s.Name,c.Cname from students AS s left jion courses AS c on s.CID1=c.CID;(左連接)
- select s.Name,c.Cname from students AS s right jion courses AS c on s.CID1=c.CID;(右連接)
- 顯示各個同學與他相對應的導師:
- select c.Name as student,s.Name as teacher from students as s,students as c where
- s.SID=c.TID;
- 顯示每一位老師及其所教授的課程;沒有教授的課程保持爲NULL:
- select t.Tname,c.Cname from tutors as t left join courses as c on t.TID=c.TID;
- 顯示每一個課程及其相關的老師,沒有老師教授的課程將其老師顯示爲空:
- select t.Tname,c.Cname from tutors as t right jion courses as c on t.TID=c.TID;
- 顯示每位同學CID1課程的課程名及其講授了相關課程的老師的名稱:
- select Name,Cname,Tname from students,courses,tutors where students.CID1=courses.CID
- and courses.TID=tutors.TID;
- 查看同學的成績及姓名,並且按升序排列:
- select students.Name,scores.Score from students,scores where students.SID=scores.SID
- order by scores.Score desc;
- 子查詢
- 挑選出courses表中沒有被students中的CID2學習的課程的課程名稱:
- select Cname from courses where CID not IN (select CID2 from students where
- CID2 is not null);
- 挑選出沒有教授任何課程的老師,每個老師及其所教授課程的對應關係在courses表中:
- select Tname from tutors where TID not in (select distinct TID from courses);
- 找出students表中CID1有兩個或兩個以上同學學習了的同一個門課程的課程名稱:
- select Cname from courses where CID in (select CID1 from students group by CID1
- having count(CID1) >=2);
- 年齡大於平均年齡的同學:(使用子查詢時,子查詢只能返回單個值):
- select Name,Age from students where Age > (select avg(age) from students);
- 查詢學生和老師各自的年齡並寫在一個表中:
- (select Name,Age from students) union (select Tname,Age from tutors);
上面的就是關於MySQL的一些基礎性總結,如果其中不對的地方還請大家指出