A quick note on SQL views.
“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.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.” – this is the
definition of a SQL view. I wish more
people would realise the importance of this definition. It essentially means that, although the view
in question may seem like a table when queried through Management Services or
something similar, it is just that – it is a result of a SQL query statement.
Too many times I have come across databases that are almost
entirely built with views because the person building the queries does not
realise this fundamentally important principle.
Don’t get me wrong – views have their place in many databases, especially
smaller ones where performance is not a major concern. The danger is when the database continues to
grow and develop and the developer / perpetrator does not change the way the
data is being presented. You will then
find that you have a SQL statement that takes longer and longer to run. The reason? You develop a query that produces
the resulting data that you were asked to provide and this queries a view. In turn, this view may query more views which
may also query more, ad infinitum.
Nested queries can be a ticking time bomb if not kept in check and the
dangers become apparent very quickly as time goes on.
If you want a report or query to run properly, my advice is to
get rid of your views. There should
never be a complex query run on a view and there are NO exceptions. Don’t listen to anyone who says different. These are people who avoid and fall in the
realm of Einstein’s advice – “if you can’t explain it simply, you don’t
understand it well enough”. I’ve met many
people like this in my time and the only advice worth giving about them is to
stay well clear. This type of person
will not help you in your endeavours.
So, my advice? Use views
sparingly and respect your users and servers.
