MySQL (ii)

View

A view is a virtual table (not a real one), which is essentially "getting a dynamic dataset from an SQL statement and naming it", which allows the user to get a result set using only "name" and use it as a table.

Temporary table Search

Select    *from    (        Select            nid,            NAME        from            tb1        WHERE            nid > 2    ) as Awhere    A. NAME > ' Alex ';

1. Create a View

--Format: CREATE VIEW name  as SQL statement CREATE VIEW v1 as Selet nid,     namefrom    awhere    nid > 4

2. Delete View

--Format: Drop View Name Drop View V1

3. Modify the View

--format: ALTER VIEW name as SQL statement alter VIEW v1 asselet A.nid,    B. namefrom    Aleft Join B on a.id = B.nidleft Join C on a.ID = C.nidwhere    a.id > 2AND C.nid < 5

4. Using views

When you use a view, you manipulate it as a table, and because the view is a virtual table, you cannot use it to create, update, and delete real tables, only for queries.

SELECT * FROM v1

Trigger

Before and after an "Add/delete/change" operation on a table if you want to trigger the behavior of a feature, you can use a trigger that customizes the behavior of the user before and after the "Add/delete/change" row of the table.

MySQL (ii)