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What is a database:

Database is the data storage and management software that interacts with the application program, and the ones that store data can also be called databases. In the past, when you did not use the database, you could only write your own data storage scheme.

What is a sql statement:

Sql statement is the command to operate on the database, also known as the database language.

Mainstream database software:

Oracle: the relational database management system developed by Oracle is currently the most widely used database software in large enterprises around the world, and its price is also the most expensive.

MySQL: developed by the Swedish company MySQL AB, it is currently a product of Oracle. MySQL is one of the most popular relational database management systems. In terms of WEB applications, MySQL is the best RDBMS (relational database management system) application software.

SQLServer: a relational database system developed by Microsoft (Microsoft). SQL Server is an extensible, high-performance database management system designed for distributed client / server computing. It combines with WindowsNT organically and provides a transaction-based enterprise information management system.

DB2:DB2 is a set of relational database management system developed by IBM Company in the United States. Its main operating environment is UNIX (including IBM's own AIX), Linux, IBM I (formerly known as OS/400), z/OS, and Windows server version. DB2 is mainly used in large-scale application systems, has good scalability, can support from mainframe to single-user environment, and can be applied to all common server operating system platforms.

In Sybase:1984, Mark B. Hiffman and Robert Epstern founded Sybase and launched the Sybase database product in 1987, which is a database based on client / server architecture. There are three main versions of SYBASE, one is the version running under the UNIX operating system, the second is the version running under the Novell Netware environment, and the third is the version running under the Windows NT environment. SYBASE 10 and SYBASE 11 for SCO UNIX are widely used in UNIX operating system.

Databases are divided into the following types:

DBMS: database management system, early database, presenting data in the form of text, cluttered and not intuitive

RDBMS: relational database management system, the current mainstream database, a database that presents data in the form of tables, and the data is intuitive:

ORDBMS: object-relational management system, relatively unpopular database, insert objects in the columns of the table, that is, object-relational database, each column can put one object.

SQL statement type: used to manipulate the data in the table

DDL: structural statements that can create, delete, modify, index, view, stored procedures, and shape structures.

DML: update data statements, specialize in manipulating data, and the operation is limited, basic manipulation of the data in the table. The main function is to add, delete, check and change, most of which are using query statements. The branch is DQL, which specializes in queries.

DCL: statements that control and manipulate the database.

Four major engines of mysql:

ISAM: advantages: read speed, small memory footprint disadvantages: do not support transaction processing

MyISAM indexing and locking functions are suitable for web development

Advantages of HEAP: operating data in memory is fast, but remember to store it on disk. Disadvantages: it takes up a lot of memory.

InnoDB advantages: supporting transaction processing has disadvantages to all basic functions: but it will be slower

Flow chart:

MySQL: the advantages are small and fast, cross-network, and multithreaded databases

You can use the engine to cluster databases:

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