MySQL Views - Use or Not Use [closed] - mysql

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I wanted to ask if View are really worth using.
From my understanding a view is really just a query and each time you query the view the view then runs its own query again to get fresh/uptodate data.
This sounds to me like 2 queries are run.
wouldn't it be faster to just run the query required and skip the view?
Please note: I would be using simple views but even it they were quite complex I assume the same principle applies.
My type of view - say 3 tables with 6 columns each - and 2 columns of each time is added into the view with a couple of maths equations to refine the data a touch.
What do others do? Skip or use them?

Answer 1

Typically Views are set up to make selects easier to understand and at the same time give guidance to the database engine on how to optimize the query. By creating a view you tell the database engine that you're going to be selecting from this frequently and to spend more time optimizing the query plan so selects from the view will be faster. The upside of this is that when it comes time to parse the query and plan the query you'll save some execution time because the optimization has already been performed. It could be as little as a few miliseconds you save, or potentially very large (for very large result sets)

Answer 2

You're correct that views are not designed to be a performance benefit in MySQL.
What they are designed to do is make other queries built on them to be simpler to read, and to make sure that other users and programmers have a better chance at using the data correctly. Think of them as a way to virtually de-normalize the data without taking the size/performance hit of actually de-normalizing the data.
Just as the most simple case, let's just take orders and line items. Each order has a line item.
The orders table might have the following columns:
ID
Status
Created_at
Paid_on
And the line_items table might have the following columns:
LI_ID
order_id
sku_id
quantity
price
What you'll find, when writing code and queries is that you are going to be doing the following join all the time -
orders
join line_items on line_items.order_id = orders.id
This could be simplified by creating a view:
create view 'order_lines' as
select * from orders
join line_items on line_items.order_id = orders.id
So your query would go from:
select orders.id, sum(price) from orders
join line_items on line_items.order_id = orders.id
where created_at >= '2011-12-01' and created_at < '2012-01-01
group by orders.id;
to:
select id, sum(price) from order_lines
where created_at >= '2011-12-01' and created_at < '2012-01-01
group by id;
The DB will execute both of these exactly the same way, but one is easier to read. Admittedly in this case, not MUCH easier to read, but easier to read and code.

Answer 3

The query optimizer is usually able to combine the view query with the query that uses the view in such a way that only a single query is run, so the objection you have to views doesn't really apply.

Answer 4

See also:
MySQL VIEW as performance troublemaker
View vs. Table Valued Function vs. Multi-Statement Table Valued Function
Should I use a view, a stored procedure, or a user-defined function?
Regards

Answer 5

Views can be provided to applications or users that needs a straight-forward view of data that isn't necessarily in one table (or limited fields from one table). That means they don't have to understand the data and how it relates -- they just get the data they need. You create the complex query, optimize it, and they just use the resulting view.