SQL statements-View

View:

What is a view, the view is actually a SQL statement, he is a query statement, you can wrap a very long SQL statement, the view can also delete the modified add, but generally do not do so, used to query on the line

The three main types of views:

MergeQueries will combine the SQL statements of the view with the external SQL statements, and then run
TemptableThe results of the query are in a temporary table and then queried
Undefined 未知Unknown algorithm

Create a View

Create View Hello as select * from Table_type_view1

Modify a View

Alter View Hello as select * from Table_type_view1 0,10

Specify the View engine

Alter algorithm=merge Viewstudentview as select sname from student

Delete a view

Delete and modify only data that is queried by the data to delete the modifications

Deop View Studentview

Association relationship:

What is an association relationship?
One column only puts one value
It is best not to add and remove columns in the development process after a tabular design is finalized
You should not display the same data in other tables when designing a table

SQL statements-View