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The many (too many?) reads of a many to many Merge Join

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SQL Server’s optimizer can choose between four different physical operators for joining data. The Merge Join operator is usually the best choice if the input data is already sorted by the join columns. It processes both inputs at the same time, every time advancing the input that has the lowest value of the join key. This algorithm, known as “balance line processing” back in the olden days of magnetic tape storage, always finds all matches with just a single pass over each of the inputs. One to many One of the most important properties in a Merge Join operator is…

Willkommen, Bienvenue, Welcome

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It may be surprising to see a word of welcome posted in December 2017, on a blog that has posts going back as far as 2006. And yet, this is my very first new blog post on this site. All the content before this post was originally published at SQLblog.com. SQLblog.com is a fantastic website that hosts many bloggers. It has hosted me for almost twelve years as well. But it was time to move house, to create a new website for the content I have planned for the future. For now, this website is just my blog. But that…
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