[MySQL learning notes 26] view

Create view

CREATE VIEW view_name[(col1,col2,…)] AS SELECT sentence [WITH [CASCADED|LOCAL] CHECK OPTION];

Query view

Look at the create statement

show create view View name ;

Inquire about

select * from View name ;

Modify the view

Mode one

CREATE OR REPLACE VIEW view_name[(col1,col2,…)] AS SELECT sentence [WITH [CASCADED|LOCAL] CHECK OPTION];

Mode two

ALTER VIEW View name ( List ) AS SELECT sentence [WITH [CASCADED|LOCAL] CHECK OPTION];

Delete view

DROP VIEW [IF EXISTS] View name ;

Insert

Inserting a view will insert it into the original table

Check options

When using WITH CHECK OPTION Clause when creating a view ,MySQL Each row that is changing is checked through the view , For example, insert , to update , Delete , To make it conform to the definition of the view .MySQL Allows you to create a view based on another view , It also checks the rules in the dependency view for consistency . In order to determine the scope of inspection ,mysql There are two options ：CASCADED and LOCAL, The default value is CASCADED.
nothing with check option when , It does not need to meet the conditions of the current view . And for the bottom view （ That is, the view for which this view is directed ）, First determine whether the bottom view has with check option sentence , Some words , According to its rules （local perhaps cascaded） Handle , If not, you do not need to meet the conditions of the bottom view .
with local check option when , You need to meet the conditions of the current view . For bottom view , It is also to see whether there is a designated with check option sentence , If any, handle it accordingly , If there is none, the conditions of the bottom view need not be met .
with cascaded check option（cascaded It can be omitted ） when , You need to meet the conditions of the current view . And for all bottom view conditions , It also needs to be met together , Even if the bottom view is not defined with check option sentence .

to update

To make the view updatable , Then the columns of the view must correspond to the columns of the original table one by one