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The following brings you mysql view knowledge related content, I believe you must have read similar articles. What's the difference between what we bring to everyone? Let's take a look at the body. I believe you will gain something after reading the knowledge of mysql view.

View concept:

A view refers to a virtual table in a computer database, whose contents are defined by a query. Like a real table, a view contains a series of named columns and rows of data. However, the view does not exist in the database as a set of stored data values. Row and column data to freely define the table referenced by the view's query, and dynamically generated when the view is referenced. For details, see the Baidu encyclopedia of the view, which has a detailed explanation of the classification and advantages of the view.

View creation:

Create view view_name as select column 1, column 2,. From table name

We can think of the view as a predefined subquery, as in the above statement, it would be quite easy to understand if we replaced create with select.

Select * from select col_1,col_2 from tbl_1 as temp

In fact, the working principle of the view is the same as the temporary table generated by this seed query, and the virtual table will be generated dynamically according to the original table only when the view is used. So the data of the view will change according to the data change of the original table.

Give an example

`create table employee (

Id int primary key auto_increment

Name varchar (20) not null

Salary decimal (10Pol 2) not null default 1000

);

Create view v_emp as select id,name from employee; `

Mysql > desc v_emp

+-+ +

| | Field | Type | Null | Key | Default | Extra | |

+-+ +

| | id | int (11) | NO | | 0 | |

| | name | varchar (20) | NO | | NULL |

+-+ +

You can see that the view v_emp we created successfully hides the employee's salary field salary

View Management Delete View

Drop view [if exists] view_name

Modify the view

Alter view v_view_name as select * from tbl_1

Modify the view structure

Alter view v_view_name (col_1,col_2...) As select a,b from tbl_1

This allows you to hide not only the table name but also the field name.

Be careful

Views support query operations best, and have certain restrictions on additions, deletions and modifications, such as views composed of multiple tables, while views created by a single table have default values or allow empty fields in the original table that are not included in the view when inserting data. Only in this way can we ensure the success of the operation.

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