[SQL Server] SQL overview

What is? SQL？

SQL Structured query language （Structured Query Language）, A device for storing 、 A computer language for manipulating or retrieving data stored in a relational database .

SQL It's a relational database system （Relation Database System） The standard language of . All relational database management systems , for example MySQL、MS Access、Oracle、Sybase、Informix、Postgres SQL and SQL Server, All use SQL As its standard database language .

Of course , They all use different SQL dialect . for example ：

• Microsoft SQL Server It uses T-SQL
• Oracle It uses PL/SQL
• Microsoft Access Medium SQL be called JET SQL （ Local format ） wait

Why use SQL？

• Allow users to access data in a relational database
• Allow the user to describe the data
• Allows you to define data in a database , And operate on it
• Allowed to pass through SQL modular 、 Library or precompiler , Embedded in other languages
• Allows users to create or delete databases and tables
• Allows users to create views in the database 、 Stored procedures and functions
• Allow users to edit tables 、 Process and view settings

Shi Hai looks back

• 1970 year ,IBM Edgar · Dr. cod proposed a database relational model , Therefore, he is called the father of relational database .
• 1974 year , Structured query language is available .
• 1978 year ,IBM Yes Codd The proposed concept has been deeply studied , And released a product called System/R Products .
• 1986 year ,IBM The first relational database prototype is developed , The prototype was then ANSI Accepted and standardized .Relational Software——Oracle The forerunner of —— Released the first commercial relational database product .

SQL technological process

In any kind of RDBMS On the implementation SQL command , The database management system will determine the best way to execute the request , And by the SQL The engine figured out how to complete the task .

This process involves a variety of components , Including query scheduler （Query Dispatcher）、 Optimization engine （Optimization Engines）、 Classic query engine （Classic Query Engine） and SQL Query engine （SQL Query Engine） wait . The classic query engine is used to deal with all non - queries SQL Inquire about , and SQL The query engine does not process logical files .

The following picture briefly illustrates SQL The architecture of ：

SQL command

Standards for interacting with relational databases SQL Command has CREATE、SELECT、INSERT、UPDATE、DELETE and DROP, These commands are divided into the following groups by purpose ：

Data definition language

Data manipulation language

Data control language