Question

I am currently writing my truly first PHP Application and i would like to know how to project/design/implement MySQL Views properly;

In my particular case User data is spread across several tables (as a consequence of Database Normalization) and i was thinking to use a View to group data into one large table:

CREATE VIEW `Users_Merged` (
name,
surname,
email,
phone,
role
) AS (
SELECT name, surname, email, phone, 'Customer'
FROM `Customer`
)
UNION (

SELECT name, surname, email, tel, 'Admin'
FROM `Administrator`
)
UNION (

SELECT name, surname, email, tel, 'Manager'
FROM `manager`
);

This way i can use the View’s data from the PHP app easily but i don’t really know how much this can affect performance.

For example:

SELECT * from `Users_Merged` WHERE role = 'Admin';

Is the right way to filter view’s data or should i filter BEFORE creating the view itself?
(I need this to have a list of users and the functionality to filter them by role).

EDIT

Specifically what i’m trying to obtain is Denormalization of three tables into one. Is my solution correct?
See Denormalization on wikipedia

Answer 1

In general, the database engine will perform the optimization for you. That means that the engine is going to figure out that the users table needs to be filtered before being joined to the other tables.

So, go ahead and use your view and let the database worry about it.

If you detect poor performance later, use MySQL EXPLAIN to get MySQL to tell you what it’s doing.

PS: Your data design allows for only one role per user, is that what you wanted? If so, and if the example query you gave is one you intend to run frequently, make sure to index the role column in users.