MySQL view explanation

What is a view ：mysql The view is a section of our Commonly used or complicated Of SQL Statement to save to the view . And alias the view , Each time we call, we can directly call our view method to execute SQL.

Create view ：

 Case code ：
    // Create view 
    CREATE VIEW  View name 
    as 
    // Query statement 
    SELECT u.* from `user` u
    LEFT JOIN user_wallet w
    ON u.id = w.user_id
    // Execution view 
    SELECT * from  View name  WHERE id=538

View modification ：

// Modify view Syntax    Method 1 
create or replace VIEW  Modified view name 
as 
SELECT w.* from `user` u
LEFT JOIN user_wallet w
ON u.id = w.user_id

// Modify view Syntax    Method 2 
ALTER VIEW  View name 
as
SELECT w.* from `user` u
LEFT JOIN user_wallet w
ON u.id = w.user_id

View and delete views ：

// Delete view , Multiple view deletions are separated by commas 
DROP VIEW v2;

// View view 

// Method 1 
DESC  View name 

// Method 2 
SHOW CREATE VIEW  View name 

View SQL Updating and inserting data ：

      I won't write code cases here , The syntax is the same as the usual insert update , Just change the name to the view name , When inserting and updating views, they are not only operating on view data , It also operates on the data in the original table , The problem to be noted is that if the fields in the original table are not viewed ( Our view also cannot insert data ), Then the data in the original table will appear null , If our field design cannot be empty, view me INSERT Will be abnormal .       

        The key functions contained in the view that cannot be updated ：distinct、group by、baving、union perhaps union all