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Inner Join

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The INNER JOIN matches every row in one table against every row in another based on common values in one or a set of columns found in both tables. This type of join operation is a filtered join. In its most basic approach an INNER JOIN acts like a nested loop where you match a key from the outer loop against a key from the inner loop.

Another way to describe an INNER JOIN is as an intersection between two rows of data. The formula uses a ∀ to indicate given any sets A and B, then A intersects (∩) B. The intersection works by linking a row of data in one table with a row of data in another table based on the values in one or more columns found in each table. In some implementations you get two copies of the column or set of column values that match, and in others you get a single copy of the matching column or set of column values.

Written by michaelmclaughlin

January 17th, 2010 at 10:24 pm

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