Difference between views and SELECT queries

Question

If views are used to show selected columns to the user, and same can be done by using

SELECT col1, col2
FROM   xyz

, what is the point of using views?

Answer 1

All answers above provide an excellent explanation for the difference between a view and a query.

The query in the question is simple to an extreme degree, and creating a view for it might be overkill. However, most queries are more complex, for example:

 ;with Orders2016 as (
    select Customers.CustomerID
         , Customers.CompanyName
         , TotalOrderAmount = sum(OD.Quantity * OD.UnitPrice)
    from Customers
             join Orders O on Customers.CustomerID = O.CustomerID
             join OrderDetails OD on O.OrderID = OD.OrderID
    where OrderDate >= '2016-01-01'
      and OrderDate < '2017-01-01'
    group by Customers.CustomerID, Customers.CompanyName
)
   , CustomersGroups as
    (
        select CustomerID
             , CompanyName
             , TotalOrderAmount
             , CustomerGroup =
            (
                case
                    when
                        TotalOrderAmount >= 0 and TotalOrderAmount < 1000
                        then 'low'
                    when TotalOrderAmount >= 1000 and TotalOrderAmount < 5000
                        then 'Medium'
                    when TotalOrderAmount >= 5000 and TotalOrderAmount < 10000
                        then 'High'
                    when TotalOrderAmount >= 10000 then 'VeryHigh'
                    end
                )
        from Orders2016
    )
select CustomerGroup
     , TotalInGroup      = Count(*)
     , PercentageInGroup = Count(*) * 1.0 / (select count(*) from CustomersGroups)
from CustomersGroups
group by CustomerGroup
order by TotalInGroup desc;

Imagine rewriting it each time you want to access data. (Or even searching through files, copy & paste). Poor time management.

Views also save us tons of time and are a way to be DRY.