The theory of Structured Query Language was proposed in 1974 and was implemented on the System R of IBM company. Because of its advantages of rich function, flexible use, simple language and so on, it is popular in the computer industry and users, and it is quickly popularized. Later, ANSI and ISO have approved SQL as the relational database language to become American and international standards.
At this point, SQL is the standard language for relational databases, and relational database systems generally support standard SQL statements. Therefore, although today's different brand relational databases have such or different discrepancy, people can operate the database through standard SQL statements, which greatly reduces the burden of users.
Although SQL is called "query language", its function is not only query, its functions include query, manipulation, definition and control four aspects, it is a comprehensive, powerful and powerful relational database language. SQL has several outstanding advantages as follows:
(1) integration. SQL can complete all activities including database definition, modification, deletion, data updating, data querying and other database lifecycle. It brings a lot of convenience to users.
(2) flexibly. There are two ways of using SQL. One is on - line interactive use; the other is in a program that embeds a high-level programming language. The grammatical structure of the two ways is unified. This will not only give the user a flexible choice, but also do not bring inconsistency.
(3) highly non process. Compared with the advanced programming language, SQL has a great advantage in the operation of the database. The use of SQL users only needs to put forward "what to do", do not know the details of the implementation, the complex process is automatically completed by the system.
(4) simple language, easy to learn and easy to use.
