sql language is often called

SQL language, often called structured query language, is a special-purpose programming language, a database query and programming language, used to access data and query, update and manage relational database systems; It is also the extension of the database script file.

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 users to specify the data storage method, nor does it require users to understand 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 extremely flexible and powerful. (Recommended study: MySQL Tutorial)

In October 1986, the American National Standards Institute standardized SQL as the standard language for relational database management systems (ANSI X3. 135 -1986), and became an international standard in 1987 with the support of the International Standards Organization. However, various popular database systems have made some modifications and expansions to the SQL specifications in their practice. Therefore, in fact, SQL between different database systems cannot be completely interchangeable.

Language Introduction

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 of embedding SQL in the fourth-generation software development tools, etc.

Supported standards

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

Other versions

The SQL language support of various databases is slightly different from the standard. This is because some products are developed before the standard. In addition, each product developer needs to extend the standard in order to achieve special performance or new features. There are more than 100 database products SQL available on microcomputers to mainframes, including DB2, SQL/DS, ORACLE, INGRES, SYBASE, SQLSERVER, DBASE IV, PARADOX, MICROSOFTACCESS, etc.

SQL language is basically independent of the database itself, the machine used, the network, and the operating system. SQL-based DBMS products can run on various computers from personal computers and workstations to LAN-based, minicomputers, and mainframes. System has good portability. It can be seen that standardization work is very meaningful. As early as 1987, some knowledgeable people predicted that the standardization of SQL was "a revolution" and "a turning point in relational database management systems."

Databases and various products use SQL as a common data access language and standard interface, which provides a common basis for interoperability between different database systems, thereby enabling heterogeneous machines and various operations. Environment sharing and porting.

In 1974, the SEQUEL language (proposed by BOYCE and CHAMBERLIN) was used in the large-scale relational database management system SYSTEM R developed by IBM's St. Joseph Research Laboratory. Later, the SQL language was developed based on SEQUEL. . S

QL language is an interactive query language that allows users to query stored data directly, but it is not a complete programming language, such as it does not have DO or FOR similar loop statements, but it can be embedded in another Among the languages, you can also borrow VB, C, JAVA and other languages ​​and send them directly to the database management system through the call level interface (CALL LEVEL INTERFACE).

SQL is basically domain relational calculus, but can implement relational algebra operations.

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