Mysql database

Catalog

1. Database concept

2. MySQL Basic operation of database

3. MySQL data type

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1. Database concept

Definition ： A collection of data , It has a unified structure and defense in a unified storage medium , It is the integration of multiple application data , And can be shared by various applications
characteristic ： Integrate 、 share

2. MySQL Basic operation of database

SQL contain 4 Parts of ：

Data query language （DQL）：
Its statement , Also known as “ Data retrieval statements ”, To get data from a table , Determine how the data is presented in the application . Reserved words SELECT yes DQL（ Also all SQL） The most used verb , other DQL The common reserved words are WHERE,ORDER BY,GROUP BY and HAVING. these DQL Reserved words are often associated with other types of SQL Statement together .

Data operation language （DML）：
Its sentences include verbs INSERT,UPDATE and DELETE. They are used to add , Modify and delete rows in the table . Also known as action query language .

Data control language （DCL）：
Its sentences are passed through GRANT or REVOKE Get permission to , Determine the access of individual users and user groups to database objects . some RDBMS You can use GRANT or REVOKE Control access to form columns .

Data definition language （DDL）：
Its sentences include verbs CREATE and DROP. Create a new table or delete a table in the database （CREAT TABLE or DROP TABLE）; Index the table, etc .DDL It includes many reserved words related to obtaining data in the human database directory . It's also part of the action query .

3. MySQL data type

type	meaning
int	integer
float	Single precision floating point 4 byte 32 position
double	Double precision floating point 8 byte 64 position
char	Fixed length character types
varchar	Variable length character types
text	Text
image	picture
decimal (5,2)	5 A valid length number , After the decimal point is 2 position