What are views in MySQL? - mysql

Question

What are views in MySQL? What's the point of views and how often are they used in the real world?

Answer 1

Normal Views are nothing more then queryable queries.
Example:
You have two tables, orders and customers, orders has the fields id, customer_id, performance_date and customers has id, first_name, last_name.
Now lets say you want to show the order id, performance date and customer name together instead of issuing this query:
SELECT o.id as order_id, c.first_name + ' ' + c.last_name as customer_name,
o.performance_date
FROM orders o inner join customers c
you could create that query as a view and name it orders_with_customers, in your application you can now issue the query
SELECT *
FROM orders_with_customer
One benefit is abstraction, you could alter the way you store the customers name, like inlcuding a middle name, and just change the views query. All applications that used the view continue to do so but include the middle name now.

Answer 2

It's simple: views are virtual tables.
Views are based on SELECT-queries on "real" tables, but the difference is that views do not store the information unlike real tables. A view only references to the tables and combines them the way SELECT says them to. This makes often used queries a lot more simplified.
Here's a simple example for you. Lets suppose you have a table of employees and a table of departments, and you'd like to see their salaries. First you can create a view for the salaries.
CREATE VIEW SALARIES
AS
SELECT e.name,
e.salary,
d.name
FROM employees AS e, deparments as d
WHERE e.depid = d.depid
ORDER BY e.salary DESC
This query lists the name of the employee, his/her salary and department and orders them by their salaries in descending order. When you've done this you can use queries such as:
SELECT * from SALARIES
On a larger scale you could make a view that calculates the average salary of the employees and lists who has a salary that's less than the average salary. In real life such queries are much more complex.

Answer 3

In mysql a view is a stored select statement
Look to this answer: MySQL Views - When to use & when not to

Answer 4

You can think of the view as a on-the-fly generated table. In your queries it behaves like an ordinary table but instead of being stored on the disk, it is created on the fly when it is necessary from a SQL statement that is defined when creating a view.
To create a view, use:
CREATE VIEW first_names AS SELECT first_name FROM people WHERE surname='Smith'
You can then use this view just as an ordinary table. The trick is when you update the table people the first_names view will be updated as well because it is just a result from the SELECT statement.
This query:
SELECT * FROM first_names
will return all the first names of people named Smith in the table people. If you update the people table and re-run the query, you will see the updated results.
Basically, you could replace views with nested SELECT statements. However, views have some advantages:
Shorter queries - nested SELECT statements make the query longer
Improved readability - if the view has a sensible name, the query is much easier to understand
Better speed - the view's SELECT statement is stored in the database engine and is pre-parsed, therefore it doesn't need to be transferred from the client and parsed over and over again
Caching and optimizations - the database engine can cache the view and perform other optimizations

Answer 5

They're a shorthand for common filters.
Say you have a table of records with a deleted column. Normally you wouldn't be interested in deleted records and hence you could make a view called Records that filters out deleted records from the AllRecords table.
This will make your code cleaning since you don't have to append/prepend deleted != 1 to every statement.
SELECT * FROM Records
would return all not-deleted records.

Answer 6

In simple words
In SQL, a view is a virtual table
based on the result-set of an SQL
statement.
A view contains rows and columns, just
like a real table. The fields in a
view are fields from one or more real
tables in the database.
You can add SQL functions, WHERE, and
JOIN statements to a view and present
the data as if the data were coming
from one single table.
Source
In addtion to this, you can insert rows in an underlying table from a view provided that the only one table is referred by the view and columns which are not referred in the view allow nulls.

Answer 7

A view is a way of pre-defining certain queries. It can be queried just like a table, is defined by a query rather than a set of on-disk data. Querying it allows you to query the table's results.
In most cases, querying a view can be seen as equivalent to using the view's defining query as a subquery in your main query. Views allow queries to be shorter and more modular (as the common parts are defined separately in the view). They also provide opportunity for optimization (although not all databases do so; I am not sure if MySQL provides any optimizations to make views faster or not).
If you update the underlying tables, queries against the view will automatically reflect those changes.