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This article mainly introduces the meaning of sql language, has a certain reference value, friends in need can refer to. I hope you will learn a lot after reading this article. Next, let the editor take you to learn about it.

Sql, which is usually called structured query language, is a special purpose programming language, a database query and programming language for accessing data and querying, updating and managing relational database systems, as well as an extension of database script files.

Structured query language is a high-level non-procedural programming language that allows users to work on high-level data structures. It does not require the user to specify the data storage method, nor does it require the user to know the specific data storage method, so different database systems with completely different underlying structures can use the same structured query language as the interface for data input and management. Structured query language statements can be nested, which makes it have great flexibility and powerful functions. (.)

In October 1986, the American National Standards Institute standardized SQL as the standard language of relational database management system (ANSI X3. It became an international standard in 1987 with the support of the International Standards Organization (ISO). However, all kinds of popular database systems have made some modifications and extensions to the SQL specification in their practice. Therefore, in fact, the SQL between different database systems can not be completely common to each other.

Brief introduction of language

Application

Structured query language SQL (STRUCTURED QUERY LANGUAGE) is the most important relational database operation language, and its influence has gone beyond the database field, and has been valued and adopted in other fields, such as data retrieval in the field of artificial intelligence, the language embedded in SQL in the fourth generation software development tools, and so on.

Support standard

SQL is an American standard for database language adopted by the American National Standards Institute (ANSI) in October 1986, and then the International Organization for Standardization (ISO) issued a formal international standard for SQL. In April 1989, ISO put forward the SQL89 standard with integrity characteristics, and in November 1992, the SQL92 standard was published. In this standard, the database is divided into three levels: basic set, standard set and complete set.

Other editions

There are slight differences in the support and standards for SQL in different databases, because some products are developed before the standards are published, and in addition, product developers need to extend the standards in order to achieve special performance or new features. There are more than 100 kinds of database products SQL from microcomputers to mainframes, including DB2, SQL/DS, ORACLE, INGRES, SYBASE, SQLSERVER, DBASE Ⅳ, PARADOX, MICROSOFTACCESS and so on.

SQL language is basically independent of database itself, machines, networks and operating systems. DBMS products based on SQL can run on various computer systems from individual man-machine and work station to local area network, minicomputer and mainframe, and have good portability. It can be seen that standardization work is very meaningful. As early as 1987, some people of insight predicted that the standardization of SQL was "a revolution" and "a turning point in relational database management systems".

Databases and all kinds of products use SQL as the common data access language and standard interface, which makes the interoperation between different database systems have a common basis, and then realizes the sharing and transplantation of heterogeneous machines and various operating environments.

In 1974, in SYSTEM R, a large-scale relational database management system developed by San Joseph Research Laboratory of IBM Company, SeQuel language (proposed by BOYCE and CHAMBERLIN) was used, and then SQL language was developed on the basis of SEQUEL. S

QL language is an interactive query language, which allows users to query and store data directly, but it is not a complete program language, such as it does not have cyclic statements like DO or FOR, but it can be embedded in another language, or it can be directly sent to the database management system through call-level interface (CALL LEVEL INTERFACE) through VB, C, JAVA and other languages.

SQL is basically a domain relational calculus, but it can be operated by relational algebra.

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