MySQL Basics - Introduction and basic instructions

introduction ： About databases

Database is used to record and manage data warehouse , Database can manage and process data faster than files , The database classification is shown in the following figure .

​ Relational database use That's ok ( Record ) Column ( Field )–> surface –> library ** To store data ; Non relational database Then Key value and other similar dictionaries ** Store data in a way . Compared with other data storage methods , with Persistent storage 、 Read and write very fast 、 Keep the data valid Other advantages . The call framework of the database is shown in the following figure .

​ SQL Is used for Relational database Instruction language of , Specific commands are divided into **DQL( Query instructions )、DML( Operating instructions )、DDL( Defined instruction )、TPL( Transaction processing )、DCL( Data control )** A few categories: .

basic SQL Instructions

Configuration complete Of MySQL, Just type... On the command line mysql -h Host name -P Port number -u user name -p password To log in MySQL.

1. Library related instructions

Instruction statement	Sentence function
create database Library name char set= Encoding mode UTF8;	Create a library Specify an encoding method （UTF8）
show create database Library name ;	Show the properties of the created library
show databases;	Display all databases
use Library name ;	Enter the specified library
select database();	Display the current library
drop database Library name ;	Delete Library

2. Table related instructions

Instruction statement	Sentence function
show tables;	Display all tables in the Library
show tables from Library name ;	Display all tables of the specified library without warehousing
create table Table name ( Name 1, Column data type constraint , Name 2, Column data type constraint , …);	Create a table The first column is the column name , Data types and constraints The second column lists , Data types and constraints …
desc Table name ;	View table structure
show create table Table name ;	View table creation statement
alter table Table name add Name Column data type ;	Add a new column to the table
alter table Table name modify Name Types and constraints ;	Modify the specified column type and constraint
alter table Table name change Original name New name Types and constraints ;	Rename the specified column and modify the column type and constraints
alter table Table name drop Name ; alter table Table name drop column Name 1 , drop column Name 2,… ;	Delete the specified column Deleting multiple columns must have column
drop table Table name ;	Delete table

2.1 data type

Data type followed by ( Specify the value ), Data size can be specified .

2.1.1 value type

type	size (bytes)	Range	purpose
TINYINT	1 byte	(-128,127)	Small integer value
SMALLINT	2 bytes	(-32 768,32 767)	Large integer value
MEDIUMINT	3 bytes	(-8 388 608,8 388 607)	Large integer value
INT or INTEGER	4 bytes	(-2 147 483 648,2 147 483 647)	Large integer value
BIGINT	8 bytes	(-9,223,372,036,854,775,808, 9 223 372 036 854 775 807)	Maximum integer value
FLOAT	4 bytes	(-3.402 823 466 E+38, -1.175 494 351 E-38), 0,(1.175 494 351 E-38, 3.402 823 466 351 E+38)	Single precision Floating point numbers
DOUBLE	8 bytes	(-1.797 693 134 862 315 7 E+308, -2.225 073 858 507 201 4 E-308), 0,(2.225 073 858 507 201 4 E-308, 1.797 693 134 862 315 7 E+308)	Double precision Floating point numbers
DECIMAL	Yes DECIMAL(M,D) , If M>D, by M+2 Otherwise D+2	Depend on M and D Value	Small value

2.1.2 Time and date type

type	size (bytes)	Format	purpose
DATE	3bytes	YYYY-MM-DD	Date value
TIME	3bytes	HH:MM:SS	Time value or duration
YEAR	1byte	YYYY	The year is worth
DATETIME	8bytes	YYYY-MM-DD HH:MM:SS	Mix date and time values

2.1.3 String type

type	size (bytes)	purpose
CHAR	0-255 bytes	Fixed length string
VARCHAR	0-65535 bytes	Variable length string
TINYBLOB	0-255 bytes	No more than 255 Binary string of characters
TINYTEXT	0-255 bytes	Text string
BLOB	0-65 535 bytes	Long text data in binary form
TEXT	0-65 535 bytes	Long text data
MEDIUMBLOB	0-16 777 215 bytes	Medium length text data in binary form
MEDIUMTEXT	0-16 777 215 bytes	Medium length text data
LONGBLOB	0-4 294 967 295 bytes	Maximum text data in binary form
LONGTEXT	0-4 294 967 295 bytes	Large text data

2.1.4 Other types

type	Range	purpose
bit	0,1,null	Generally used as a mark
enum	Specify the object range , Co ownership 0-65535	2 byte , Integer management , Subscript from 1 Start
set	Specify the object range , Co ownership 0-64	8 byte , Shift operation management , Subscript from 1 Start

2.2 constraint

name	purpose
primary key	Primary key
foreign key	Foreign keys
not null	Non empty
unique	The only value
default 0	The default value is
auto_increment	Automatic growth , You can use 0,null,default placeholder
data type unsigned	Unsigned type

3. Data related instructions

Instruction statement	Sentence function
insert into Table name ( Name ) values( Corresponding data ),( Corresponding data ),…;	Add data to the table , No column name defaults to all columns , Multiple groups of data can be inserted at one time
update Table name set Name 1= value , Name 2= value ,… where constraint condition ;	Update the value of the specified column under the constraint , Unconstrained means all
seclect * from Table name where constraint condition ;	Display all qualified data in the table , Unconstrained means all
seclect Name 1 as Alias , Name 2 as Alias ,… from Table name where constraint condition ;	Display the data of all qualified specified columns in the table , Alias can be specified for the name of the column , The order of arrangement is code order
delete from Table name where constraint condition ;	Delete all qualified data in the table , Unconstrained means all
alter table Table name add Name bit default 0; update Table name set Name =1 where constraint condition ;	Add delete marks to the table , Mark the data to be deleted as 1, Don't really delete data

4. Other instructions

Instruction statement	Sentence function
select getdata();	View current time
select @@version;	Check out the current version
source sql File address ;	Import run sql file