The three common functions of SQL language are: 1. Data definition; it can define the three-level schema structure of the database, namely the external schema, global schema and internal schema structure. 2. Data manipulation; including data insertion, deletion, modification and query functions for basic tables and views. 3. Data control; mainly controlling user access rights to ensure system security.
SQL language is a structured query language that can store data, update and query databases. SQL language has a unified style, is highly non-procedural, and is easy to learn and use. Features.
SQL language has three common functions: data definition, data operation, and data control.
1. The data definition function of SQL
can define the three-level schema structure of the database, namely the 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. The data manipulation function of SQL
includes data insertion, deletion and modification of basic tables and views, especially the 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.
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