The full name of SQL is "Structured Query Language", which is the earliest query language developed by IBM's San Jose Research Laboratory for its relational database management system System R. Its predecessor is SQUARE language. SQL language is simple in structure, powerful in function and easy to learn, so it has been widely used since 198 1 was introduced by IBM in. Now, both large database management systems such as Oracle, Sybase, Informix and SQL Server, and database development systems commonly used on microcomputers such as Visual Foxporo and PowerBuilder support SQL as the query language.

SQL is an advanced non-procedural programming language, which allows users to work on advanced data structures. He doesn't need users to specify the storage mode of data, and he doesn't need users to know the specific storage mode of data, so different database systems with completely different underlying structures can use the same SQL language as the interface for data input and management. It takes the recordset as the manipulated object, and all SQL statements accept the recordset as input and return it as output. This set feature allows the output of one SQL statement as the input of another, so the SQL language can be nested, which makes it very flexible and powerful. In most cases, it is necessary to write a single event of a large program in other languages, and only one SQL statement is needed to achieve the goal, which also means that very complicated statements can be written in SQL language.

SQL is also an extension of the database file format.

SQL language consists of four parts:

Data query language (SELECT statement)

Data manipulation language (insert, update, delete statements)

Data definition languages (such as CREATE, DROP and other statements)

Data control languages (such as commit, rollback and other statements)

From "http://zh.wikipedia.org/wiki/SQL"