Functions of sql language
The functions of sql language
SQL hasdata definition,data manipulationandData control function.
1. SQL data definition function
can define the three-level schema structure of the database, namely external schema, global schema and internal schema structure. In SQL, the external schema is called View, and the global schema is referred to as Schema. The internal schema is automatically implemented by the system based on the database schema, and generally does not require user intervention.
2. SQL data manipulation function
Includes data insertion, deletion and modification of basic tables and views, especially with strong data query function.
3. The data control function of SQL
is mainly to control the user's access rights to ensure the security of the system.
PHP Chinese website has a large number of free SQL tutorials, everyone is welcome to learn!
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