At present, the common database management systems mainly include Oracle, MySQL, SQL Server, Mongodb, etc. Among these databases, the first three are relational databases, while Mongodb is a non-relational database.
1.Oracle
Oracle is a relational database management system from Oracle Corporation. It is a product that has been in the leading position in the database field. It can be said that Oracle database system is a popular relational database management system in the world. The system is portable, easy to use and powerful, and it is suitable for all kinds of large, medium, small and microcomputer environments. It is a highly efficient and reliable database solution that adapts to high throughput.
The structure of Oracle includes the internal structure, external storage structure, internal storage structure and process structure of the database. In Oracle, database not only refers to the physical data, but also includes the programs that process these data, i.e. DBMS itself. oracle provides development and design tools such as PL/SQL, Designer2000, and Foms.
In addition to storing data in a relational format, Oracle supports object-oriented structures (such as abstract data types). An object can be linked to and contain other objects, and an object view can be used to support object-oriented interface data without making any changes to the table.
Whether object-oriented structure or relational structure, Oracle Database stores its data in physical data files. The database structure provides a logical diagram of data stored in files, allowing different types of data to be stored separately, and these logical divisions are the tablespaces. In Oracle, in addition to the files for storing data, there are DBMS code files log files and some other control files, trace files, etc. External storage structure mainly includes tablespace and file structure.
Oracle database uses two types of memory structures in operation, which are system global area and program global area. The system global area is the memory area where system data is stored when the database is running, and it is shared by all server processes and client processes. The program global area is a single storage for data and control information that Oracle processes need when they are working, and the program global area cannot be shared.
2. MYSQL
MYSQL is a relational database management system developed by the Swedish company MYSQL AB, currently part of the Oracle family of products. MYSQL is currently one of the most popular relational database management systems and is used by a large number of small web applications.
MYSQL is a relational database management system. A relational database stores data in different tables instead of putting all data in one big warehouse, which increases speed and improves flexibility.
The SQL language used in MYSQL is the most common standardized language used to access databases. MYSQL software has a dual licensing policy and it is divided into community and commercial versions. Due to its small size, speed, low total cost of ownership and especially the open source feature, MSQL is generally chosen as the website database for the development of small and medium-sized websites.
3. SQLServer
SQL Server is a database product from Microsoft. The distributed architecture of SQL Server I separates application access to the database from the database engine. The core database server of SQL Server runs on top of a Windows-based server. The Windows-based server is typically connected to multiple client systems via an Ethernet LAN. These client systems are typically PCs running SQL Server client software. These PCs can be either standalone desktop systems or platforms for other web services, such as IIS Web servers.
SQL Server is tightly integrated with popular development tools and desktop applications, for example, SQL Server databases can be accessed from client applications developed in VisualBasic, Visual C+, Powerbuilder, Delphi Visual Foxpro, and many other PC development environments. SQL Server is compatible with several data access interfaces used by popular development tools, for example, through Microsoft JET Engine and Data Access Objects (DAO) Remote Data Objects (RDO). Activex Data Objects (ADO), OLE DB, ODBC (OpenDatabase Connectivity) SQL Server’s built-in Db-library, and third-party development tools to access SQL Server databases. For seamless desktop access, SQL Server uses OLE DB providers and ODBC drivers that allow access from any ODBC or OLE DB-compatible desktop
applications to access SQL Server databases. OLE DB and ODBC can open SQL Server databases for specific queries, data analysis, and custom reports from hundreds of desktop applications of simplified design. Desktop integration reduces the need for custom programming efforts. SQL Server support for ODBC allows other platforms, such as Macintosh or various Unix systems, to access SQL Server databases.
The four basic server components of SQL Server include Open Data Services, MS SQL server, SQLServer Agent, and MSDTC.
4. Mongodb
Mongodb is a database based on distributed file storage. It is written in C++. It aims to provide scalable and high performance data storage solution for web applications.
Mongodb is a product between relational and non-relational databases, and is the most feature-rich and relational-like among non-relational databases. It supports a very loose data structure, similar to Json’s bson format, so it can store more complex data types. The biggest feature of Mongo is that it supports a very powerful query language, whose syntax is somewhat similar to the object-oriented query language, and can achieve almost most of the functions similar to the single-table query of a relational database, and also supports indexing of data.