| [Member (365WT)]answers [Chinese ] | Time :2019-11-13 | From a user perspective, a view looks at the data in the database from a specific perspective. From the inside of the database system, a view is a virtual table defined by a query consisting of SELECT statements. From the inside of the database system, the view is composed of data from one or more tables. From the outside of the database system, the view is like a table. Views can be queried, but they cannot be added, deleted, or modified.
A view is a virtual table whose contents are defined by a query. Like a real table, a view acts like a filter. The filter that defines the view can come from one or more tables of the current or other database, or other views. Distributed queries can also be used to define views that use multiple heterogeneous source data.
A view is a SQL statement of a query stored in a database. It is mainly for two reasons: for security reasons, the view can hide some data, such as: social insurance fund table, you can use the view to display only the name, address, and not display social insurance. Another reason, such as number and salary, is that it makes complex queries easy to understand and use.
View: The way you view a graphic or document.
Once the view is defined, it is stored in the database. The corresponding data is not stored in the database as in the table. The data seen through the view is only the data stored in the basic table. The operations on the view are the same as the operations on the table, which can be queried, modified (with certain restrictions), and deleted.
When the data seen through the view is modified, the data of the corresponding basic table also changes, and if the data of the basic table changes, the change can be automatically reflected in the view. |
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