MySql速查-1-数据库基本操作

MySql is RDBMS（Relational Database Management System）

创建连接mysql的用户

% mysql -p -u root

mysql> CREATE USER ‘sampadm‘@‘localhost‘ IDENTIFIED BY ‘secret‘;

mysql> GRANT ALL ON sampdb.* TO ‘sampadm‘@‘localhost‘

连接mysql

mysql -h host_name -p -u user_name

退出mysql

mysql> quit

执行mysql

mysql> Select Now(),User(),Version();

mysql> Select Now(),User(),Version()\g // ; \g 终止语句

mysql> Select Now(),User(),Version()\G //竖排显示，每行一个值

脚本执行

% mysql < myscript.sql

% mysql sampdb < create_member.sql

创建数据表

mysql> CREATE TABLE member

(

member_id INT UNSIGNED NOT NULL AUTO_INCREMENT,

PRIMARY KEY (member_id),

first name VARCHAR(20) NOT NULL,

last name VARCHAR(20) NOT NULL,

suffix VARCHAR(5) NOT NULL,

expiration DATE NULL

);

查看表结构

mysql> DESCRIBE member;

显示特定列

mysql> SHOW COLUMNS FROM member LIKE ‘%name‘;

列出表

mysql> SHOW TABLES;

% mysqlshow sampdb

列出数据库

mysql> SHOW DATABASE;

% mysql show

插入数据行

mysql> CREATE TABLE student

(

name VARCHAR(20) NOT NULL,

sex ENUM(‘F‘,‘M‘) NOT NULL,

student_id INT UNSIGNED NOT NULL AUTO_INCREMENT,

PRIMARY KEY (student_id)

)ENGINE = InnoDB

mysql> INSERT INTO student VALUES(‘Alex‘,‘M‘,NULL);

mysql> INSERT INTO student VALUES(‘Alex‘,‘M‘,NULL),(‘Bob‘,‘F‘,NULL); //括号内包含所有列

mysql> INSERT INTO student (name,sex) VALUES(‘Alex‘,‘M‘);

加载数据文件

mysql> LOAD DATA LOCAL INFILE ‘member.txt‘ INTO TABLE member;

% mysqlimport --local samdb member.txt

检索信息

书定顺序,Select--From--Where--Group by--Having--Order by

执行顺序,From--Where--Group by--Having--Select--Order by

NULL值表示‘无数据‘，不能与‘有数据‘的值比较

LIMIT number，限制显示行

日期函数，YEAR(),MONTH(),DAYOFMONTH()

变量，@variable

mysql> SELECT @birth:=birth FROM student where name=‘Bob‘;

mysql> SELECT name FROM student WHERE birth<@birth ORDER BY birth;

mysql> SET @today=CURDATE();

mysql> SET @one_week_ago:=DATE_SUB(@today,INTERVAL 7 DAY);

统计信息

DISTINCT,清除重复信息

COUNT(*),计数所有行

COUNT(数据列)，非NULL行

mysql> SELECT state,COUNT(*) FROM president GROUP BY status ORDER BY count DESC LIMIT 4;

多表联结

left join(左联接) 返回包括左表中的所有记录和右表中联结字段相等的记录

right join(右联接) 返回包括右表中的所有记录和左表中联结字段相等的记录

inner join(等值连接) 只返回两个表中联结字段相等的行

exists 与 in 最大的区别在于 in引导的子句只能返回一个字段，比如:

select name from student where sex = ‘m‘ and mark in (select 1,2,3 from grade where ...),

in子句返回了三个字段，这是不正确的，exists子句是允许的，但in只允许有一个字段返回，在1，2，3中随便去了两个字段即可

删除数据行

DELETE FROM tbl_name WHERE which rows to delete;

更新数据行

UPDATE tbl_name SET which columns to change WHERE which rows to update;

简化链接过程

1. ~/.my.cnf

[client]

host=server_host

user=your_name

password=your_pass

2. 命令历史

% !my //最近使用过的命令

3. alias sampdb ‘mysql -h host_name -p -u sampadm sampdb‘

聚合函数,MIN(),MAX(),SUN(),AVG()

创建数据库

CREATE DATABASE [IF NOT EXISTS] db_name [CHARACTER SET charset][COLLATE collation];

删除数据库

DROP DATABASE db_name;

变更数据库

ALTER DATABASE [db_name][CHARACTER SET charset][COLLATE collation];