Subqueries, Real and Apparent

Part III – A Look at a “Physical” Subquery Perhaps I am being a little loose in my terminology, since there really isn’t a query operator called “subquery”. When I say “physical subquery” I am referring to those correlated subqueries where the subquery portion must be executed again and again, once for every row returned […]
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Subqueries, Real and Apparent

Part II – The Table Spool In the previous installment, we looked at a very simple logical subquery that SQL Server executed as a physical join. We shall now take a look at a somewhat more complicated query and see what SQL Server does with it. In this query, we would like to get a […]
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Subqueries, Real and Apparent

As a part of our continuing study of SQL Server query plans, we’re going to take a look at some subqueries. This is particularly important, since subqueries are the subject of some fair amount of folklore, and it is important to separate fact from myth. It’s not uncommon to hear someone say “Joins are better […]
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How to apply Logistic Regression using Excel

Logistic regression is one of the most important techniques in the toolbox of the statistician and the data miner. In contrast with multiple linear regression, however, the mathematics is a bit more complicated to grasp the first time one encounters it. We’re going to gain some insight into how logistic regression works by building a […]
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SQL Server: Some Quirks in the Cache, Part II

Some Surprising Traits of SQL Server Query Caching In the previous section<link SQL Server: Some Quirks In the Cache Part 1>, we saw that it is easy to observe query execution plans being entered into the procedure cache by SQL Server. Now that the tools are in place, we will observe some unexpected behavior of […]
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