View, Map Recognition

View, Map Recognition
Purpose: 1. simplify user operations and simplify data. Many data services in the table are relatively redundant. Developers make complex statements into a view, so that other people can directly call the table without the need to write complex SQL statements for query. Views only operate on virtual tables. You do not need to know how to implement virtual tables. 2. added security. Define different views for different users to protect confidential files. 3. directly using the view when the logical Independence Program uses the database can avoid the re-design of the program caused by changes in the table structure. When the database is restructured, your application will not be affected because it operates on The View. 4. Flexibility different users view the same data in different ways, and the view allows different types of users to share data. 5. Clearer query expression
E. g create view vmg as select Sno, Max (Gade) Mgrade from SC GROUP BY Sno;
Select SC. Sno, Cno from SC, vmg where SC. Sno = VMG. Sno and SC. Gade = VMG. Mgrade;
What is a view?

A view is an SQL statement stored in a database. It is mainly for two reasons: security reasons. A view can hide some data, such as the Social Insurance Fund table, you can use the view to display only the name and address, but not the social insurance number and wage number. Another reason is that complex queries are easy to understand and use.
View: displays images or documents.

A view is a table exported from one or more tables or views. Its structure and data are based on table queries. Like a table, a view also contains several defined data columns and multiple data rows. However, in essence, these data columns and data rows come from the referenced table.
Therefore, a view is not a basic table that actually exists, but a virtual table. The data of the view is not actually stored in the database in the view structure, but in the table referenced by the view.
Once defined, the view is stored in the database. The corresponding data is not stored in the database as the table. The data displayed in the view is only stored in the basic table. Operations on a view are the same as those on a table. You can query, modify (with certain restrictions), and delete a view.
When you modify the data seen through the view, the data of the corresponding basic table also needs to change. At the same time, if the data of the basic table changes, this change can also be automatically reflected in the view.
View has many advantages, mainly manifested in:
• Centralized Viewpoint
• Simplified operations
• Custom Data
• Merge and split data
• Security

What is a view?

A view is an SQL statement stored in a database. It is mainly for two reasons: security reasons. A view can hide some data, such as the Social Insurance Fund table, you can use the view to display only the name and address, but not the social insurance number and wage number. Another reason is that complex queries are easy to understand and use.
View: displays images or documents.

A view is a table exported from one or more tables or views. Its structure and data are based on table queries. Like a table, a view also contains several defined data columns and multiple data rows. However, in essence, these data columns and data rows come from the referenced table.
Therefore, a view is not a basic table that actually exists, but a virtual table. The data of the view is not actually stored in the database in the view structure, but in the table referenced by the view.
Once defined, the view is stored in the database. The corresponding data is not stored in the database as the table. The data displayed in the view is only stored in the basic table. Operations on a view are the same as those on a table. You can query, modify (with certain restrictions), and delete a view.
When you modify the data seen through the view, the data of the corresponding basic table also needs to change. At the same time, if the data of the basic table changes, this change can also be automatically reflected in the view.
View has many advantages, mainly manifested in:
• Centralized Viewpoint
• Simplified operations
• Custom Data
• Merge and split data
• Security