Mysql -- view,

Mysql -- view,
1. view features

When a view comes from multiple basic tables, data cannot be added or deleted.

2. Create a view

Although a view can be viewed as a virtual table, it does not physically exist, that is, the database management system does not have a dedicated location to store data for the view. According to the view concept, we can find that its data comes from the query statement. Therefore, the view creation syntax is:

• Syntax:

• Example:

Create various views

(1) encapsulate the view of query statements Using Aggregate functions (SUM, MIN, MAX, COUNT, etc.

The student table is as follows:

(2) encapsulates the view for implementing the order by query statement.

3. view 1. view with show tables statements

2. DESCRIBE | DESC view View Design Information

4. delete a view

• Syntax:

• Example:

5. Modify VIEW 1. create or replace view statement modify VIEW

• Syntax:

• Example:

2. ALTER statement modification View

• Syntax:

• Example:

6. Use the view to modify basic table 1. Search (query) data

Querying data through a view is exactly the same as querying through a table, but querying through a view is safer, simpler, and easier to use than querying a table. In specific implementation, you only need to replace the table name with the view name.

• Syntax:

• Example:

2. operate basic table data using views

You can not only query data in a view, but also update (add, delete, and update) the view. Because the view is a "virtual table", the index updates the View data. In fact, the basic table data is updated.

When updating View data, pay attention to the following two points:

(1) adding, deleting, and updating View data directly affects basic tables.

(2) When a view comes from multiple basic tables, data cannot be added or deleted.

• Add data operation

After execution:

• Delete data