If Inner Join can be thought of as Cross Join but filtering out the records satisfying the condition

Posted by Jian Lin on Stack Overflow See other posts from Stack Overflow or by Jian Lin
Published on 2010-04-25T11:31:34Z Indexed on 2010/04/25 11:43 UTC
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outer-join

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inner-join

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cross-join

If an Inner Join can be thought of as a cross join and then getting the records that satisfy the condition, then a LEFT OUTER JOIN can be thought of as that, plus ONE record on the left table that doesn't satisfy the condition.

In other words, it is not a cross join that "goes easy" on the left records (even when the condition is not satisfied), because then the left record can appear many times (as many as how many records there are in the right table).

So the LEFT OUTER JOIN is the Cross JOIN with the records satisfying the condition, plus ONE record from the LEFT TABLE that doesn't satisfy the condition.

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