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POIs it possible to set up a sql view so that any joins are only performed when required?
 

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  1. POIs it possible to set up a sql view so that any joins are only performed when required?
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    <p>I'm having some trouble with view performance. Specifically some expensive joins being performed when they are not required to be. I've managed to reduce the problem to the simplest case, and have used the AdventureWorks sample database to create the following view, which pulls together a persons name and email address.</p> <pre><code>create view PersonDetails_View as select P.FirstName, P.LastName, A.EmailAddress from Person.Person P left outer join Person.EmailAddress A ON P.BusinessEntityID = A.BusinessEntityID </code></pre> <p>If I run the following query against this view:</p> <pre><code>select FirstName from PersonDetails_View </code></pre> <p>The query that is generated is equal to that of:</p> <pre><code>select P.FirstName from Person.Person P left outer join Person.EmailAddress A ON P.BusinessEntityID = A.BusinessEntityID </code></pre> <p>In this query there is an unnecessary join being performed. I know why it is happening - If there are multiple <code>EmailAddress</code> entries per <code>Person</code> row, the results will be different. However in this particular case the mapping is 1-1, and always will be. Is there a way to prevent this join happening, so that the generated query is equal to the following?</p> <pre><code>select P.FirstName from Person.Person P </code></pre> <p>(This simple case does look like micro optimization, but I have properly profiled and identified unnecessary joins in a view as a performance problem in my situation - I promise!)</p>
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    1. COMaybe you just should use the latest query (from person table, not from persondetails_view) for person data then? I would identify using persondetails_view in this scenario as unneccessary either ;)
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    2. COAgain, I broke this down to the simplest example that I could. I felt that posting a large sql view which joins upwards of 10 tables at a time would be needlessly complex for the question.
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