MySQL's past and present life, Hello, MySQL

1. What is a database ？

database （Database） It's organized according to the data structure 、 Warehouse for storing and managing data .

Each database has one or more different API Used to create , visit , management , Search and copy saved data .

We can also store data in files , But reading and writing data in files is relatively slow .

therefore , Now we use a relational database management system （RDBMS） To store and manage large amounts of data . The so-called relational database , It's a database based on a relational model , With the help of set algebra and other mathematical concepts and methods to deal with the data in the database .

MySQL database

MySQL Is a relational database management system , The Swedish MySQL AB Companies to develop , At present belongs to the Oracle company .MySQL It's an associated database management system , The associated database keeps the data in different tables , Instead of putting all the data in one big warehouse , This increases speed and flexibility .

• MySQL It's open source. , At present, it belongs to Oracle Its products .
• MySQL Support large databases . Can handle large databases with tens of millions of records .
• MySQL standards-of-use SQL Data language form .
• MySQL Can run on multiple systems , And support multiple languages . These programming languages include C、C++、Python、Java、Perl、PHP、Eiffel、Ruby and Tcl etc. .
• MySQL Yes PHP Have good support ,PHP Is very suitable for Web Application development .
• MySQL Support for large databases , Support 5000 Data warehouse of ten thousand records ,32 Bit system table files can support 4GB,64 The largest table file supported by bit system is 8TB.
• MySQL It can be customized , Adopted GPL agreement , You can modify the source code to develop your own MySQL System .

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2.RDBMS The term

Before we start to learn MySQL Before database , Let's get to know RDBMS Some of the terms ：

• database : A database is a collection of related tables .
• Data sheet : A table is a matrix of data . A table in a database looks like a simple spreadsheet .
• Column : A column of ( data elements ) Contains the same type of data , For example, postal code data .
• That's ok ： a line （= Tuples , Or record ） It's a set of related data , For example, a data subscribed by a user .
• redundancy ： Store twice as much data , Redundancy reduces performance , But it improves the security of the data .
• Primary key ： The primary key is unique . A data table can only contain one primary key . You can use the primary key to query data .
• Foreign keys ： Foreign keys are used to associate two tables .
• Composite key ： Composite key （ Composite key ） Use multiple columns as an index key , Generally used for Composite Index .
• Indexes ： Use indexes to quickly access specific information in database tables . An index is a structure that sorts the values of a column or columns in a database table . A catalogue similar to a book .
• Referential integrity : Referential integrity requires that nonexistent entities cannot be referenced in a relationship . And entity integrity is the integrity constraint that a relational model must satisfy , The purpose is to ensure data consistency .

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3.Mysql Database data structure

• Header (header): The name of each column ;
• Column (col): A collection of data of the same data type ;
• That's ok (row): Each line is used to describe the specific information of a record ;
• value (value): Details of the line , Each value must be of the same data type as the column ;
• key (key): The value of the key is unique in the current column .

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4.SQL The classification of sentences

• DDL： Data query language select
• DML： Data operation language insert delete update
• DDL： Data definition language create drop alter Structure of main operation table , Not data
• TCL： Transaction control language commit rollback
• DCL： Data control language grant revoke

Copyright notice ： This tutorial is based on the rookie tutorial