mysql - database operations and data attributes

Database operations

Start mysql, macby brewinstalling mysqlstart later. windowYou need to manually configure


mysql.server start


net start mysql

// login user name -u root -p superuser password
 mysql -uroot -p

// Exit
 mysql> q

// switch to learn the database
 mysql> use learn

MySQL statement specification

Keywords and function names are all uppercase
Database names, table names, field names all lower case
SQL statements must end with a semicolon

// create database-8 default encoding UTF
 the CREATE DATABASE IF the NOT EXISTS T1;

// Create gbk coding database
 CREATE DATABASE IF NOT EXISTS t2 CHARACTER SET gbk;

// Create a database t1 show command
 SHOW CREATE DATABASE t1;

// Check database
 SHOW DATABASES;

// delete the database
 DROP DATABASE IF EXISTS t1;

type of data

Integer

MySQL Data Types	meaning	(Signed)
tinyint(m)	1 byte	Range (-128 to 127)
smallint(m)	2 bytes	Range (-32768 to 32767)
mediumint(m)	3 byte	Range (~ -8388608 8388607)
int(m)	4 bytes	Range (-2147483648 to 2147483647)
bigint(m)	8 bytes	Range (18 + -9.22 * 10 th)

For example, we store the age range is 0-100, then we can use TINYINTto store

Float (float and double)

MySQL Data Types	meaning
float(m,d)	Total single precision floating point precision of eight bits (4 bytes) m number, d decimal places
double(m,d)	The total 16-bit double precision floating point precision (8 bytes) m number, d decimal places

Field is defined as a set float (6,3), if a number is inserted 123.45678, actually stored in the database is 123.457, but also the total number of the actual subject, i.e., six. The integer portion of the maximum is three, if the number of inserted 12.123456, 12.1234 is stored, if inserted 12.12, storage is 12.1200.

String (char, varchar, _text)

MySQL Data Types	meaning
char(n)	Fixed length, up to 255 characters
varchar(n)	Fixed length, up to 65,535 characters.
tinytext	Variable length, up to 255 characters
text	Variable length, up to 65,535 characters.
mediumtext	Variable length, a maximum power of 24 characters -1 2
longtext	Variable length, up to 32 characters power of 2 -1

charAnd varchar:

1. char(n)If the stored number of characters is less than n, it places the space up, and then remove the spaces of the query. Char type is stored so the end of the string can not have spaces, varcharis not limited thereto.

2.char(n) 固定长度，char(4)不管是存入几个字符，都将占用4个字节，varchar是存入的实际字符数+1个字节（n<=255）或2个字节(n>255)，

所以varchar(4),存入3个字符将占用4个字节。

3.char类型的字符串检索速度要比varchar类型的快。
varchar和text：

1.varchar可指定n，text不能指定，内部存储varchar是存入的实际字符数+1个字节（n<=255）或2个字节(n>255)，text是实际字符数+2个字

节。

2.text类型不能有默认值。

3.varchar可直接创建索引，text创建索引要指定前多少个字符。varchar查询速度快于text,在都创建索引的情况下，text的索引似乎不起作用。

5.二进制数据(_Blob)

1._BLOB和_text存储方式不同，_TEXT以文本方式存储，英文存储区分大小写，而_Blob是以二进制方式存储，不分大小写。

2._BLOB存储的数据只能整体读出。

3._TEXT可以指定字符集，_BLO不用指定字符集。

日期时间类型

MySQL数据类型	含义
date	日期 ‘2008-12-2’
time	时间 ‘12:25:36’
datetime	日期时间 ‘2008-12-2 22:06:44’
timestamp	自动存储记录修改时间

数据类型的属性

MySQL关键字	含义
NULL	数据列可包含NULL值
NOT NULL	数据列不允许包含NULL值
DEFAULT	默认值
PRIMARY KEY	主键
AUTO_INCREMENT	自动递增，适用于整数类型
UNSIGNED	无符号
CHARACTER SET name	Specify a character set

Original: Big Box mysql - database operations and data attributes