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July 2006 - Posts

Nested Loops Join

SQL Server supports three physical join operators: nested loops join, merge join, and hash join. In this post, I’ll describe nested loops join (or NL join for short). The basic algorithm In its simplest form, a nested loops join compares each row from
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Introduction to Joins

Joins are one of the most important operations performed by a relational database system. An RDBMS uses joins to match rows from one table with rows from another table. For example, we can use joins to match sales with customers or books with authors.
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Index Examples and Tradeoffs

The optimizer must choose an appropriate “access path” to read data from each table referenced in a query. The optimizer considers many factors when deciding which index to use, whether to do a scan or a seek, and whether to do a bookmark lookup. These
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Seek Predicates

Before SQL Server can perform an index seek, it must determine whether the keys of the index are suitable for evaluating a predicate in the query. Single column indexes Single column indexes are fairly straightforward. SQL Server can use single column
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