SQL is the abbreviation of English structured query language, which is translated into structured query language. SQL was first implemented on the database management system System R developed by IBM. Because it is close to spoken English, easy to learn, rich in functions and flexible to use, it is widely supported. After continuous development, improvement and expansion, SQL was determined by the American National Bureau of Standards (ANSI) as the American standard of relational database language, and was later adopted by the International Organization for Standardization (ISO) as the international standard of relational database language. Now all database vendors have launched their own database management systems supporting SQL, such as Microsoft's SQL Server, IBM's DB2, ORACLE, Sybase, Informix and so on.

SQL language has the following characteristics:

1. Synthesis

Although SQL is called structured query language, it can actually realize all functions of data query, definition, manipulation and control. It integrates data definition language DDL, data manipulation language DML and data control language DCL(Data control 0 l) of relational database into one language.

2. Highly non-programmed

To manipulate data in SQL language, you only need to indicate "what to do" instead of "how to do it". The selection of access path and the execution of operation are automatically completed by the database management system.

3. Two usages and unified grammatical structure

SQL language is both an independent language and an embedded language. As an independent language, it can be used alone, and users can directly input SQL commands on the terminal to operate the database.