Database objects: view learning records

Common database objects
surface
The data dictionary ： Just check without modifying
constraint ：
View ：
Indexes ：
stored procedure ：
Storage function ：
trigger ：

View
Views are built on existing tables , Existing tables are called base tables
The advantages of views simplify queries
Views are generally used on large projects , Can control data and access .
Create a view , For single table

CREATE VIEW vu_emp1
AS
SELECT employee_id,last_name,salary
FROM emps

Based on multiple tables

Use the view to format the data

CREATE VIEW abc AS
SELECT CONCAT(last_name,‘(’,department_name,‘)’) FROM emps e JOIN depts d ON e.department_id = d.department_id

SELECT * FROM abc

Create views based on views

View view

There are four ways to view

View view show tables
View view structure describe xx
View the attribute information of the view ：SHOW TABLE STATUS LIKE ‘abc’
View the detailed definition information of the view

Changes to the view will affect the data in the table

Generally, the update of view will affect the data , There are also situations that will not be updated
Modify the view , Delete view

CREATE OR REPLACE VIEW vu_emp1
AS
SELECT email,last_name,employee_id FROM emps
Modify the view
DROP VIEW vu_empl