MySQL Database foundation

1. Operating the database

1.1 Displays all current databases

show databases

1.2 Create database

create database Library name

1.3 Using a database

use database

1.4 Delete database

drop database Library name

2. Common data types

2.1 value type

It can be divided into integer type and floating point type

data type	size	explain	Corresponding java The type of
bit[(M)]	M The specified number of digits is one by default	Binary system ,M Range from 1 To 64, The storage range is 0 To 2^M-1	Commonly used Boolean Corresponding bit, The default is 1 position , That is, it can only be saved 0 or 1
tinyint	1 byte		Byte
smallint	2 byte		Short
int	4 byte		Integer
bigint	8 byte		Long
float(M,D)	4 byte	Single precision ,M Length ,D Specify the minimum number of digits . Loss of accuracy will occur	Float
double(M,D)	8 byte		Double
decimal(M,D)	M/D Maximum +2	Double precision ,M Specify the length ,D It means the number of decimal places . Exact value	BigDecimal
numeric(M,D)	M/D Maximum +2	and decimal equally	BigDecimal

2.2 String type

data type	size	explain	Corresponding java The type of
varchar(size)	0-65535 byte	Variable length string	String
text	0-65535 byte	Long text data	String
mediumtext	0-16 777 215 byte	Medium long text data	String
blob	0-65535 byte	Long text data in binary form	byte[]

2.3 The date type

data type	size	explain	Corresponding java The type of
datetime	8 byte	Range from 1000 To 9999 year , No time zone retrieval and conversion .	java.util.Date java.sql.Timestamp
timestamp	4 byte	Range from 1970 To 2038 year , Automatically retrieve the current time zone and convert it .	java.util.Date java.sql.Timestamp

3. The operation of the table

When using tables, you must first select the database
ues database Library name

3.1 View all tables

show tables

3.2 View table structure

desc Table name

3.3 Create table

create table Table name ( Built in attribute name Data storage mode , Built in attribute name Data storage mode . . . . . .)

3.4 Delete table

drop table Table name

Be careful !!!

The above mentioned deletion operation must be used with caution !!!
Because once deleted , Can't recover , Unless backed up in advance !!!