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sqlclarify
Yak Posting Veteran
56 Posts |
 Posted - 2008-09-17 : 17:20:41
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| I have 5 tables. A,B,C,D,EI have joined them in the following way..A->BB->CC->DD->EIf I join them as A->BA->CA->DA->Ewill that change the meaning of the query? |
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jezemine
Master Smack Fu Yak Hacker
2886 Posts |
Posted - 2008-09-17 : 18:27:13
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it depends on what columns you are joining on.
elsasoft.org |
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sqlclarify
Yak Posting Veteran
56 Posts |
Posted - 2008-09-19 : 13:29:52
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| A contains the foreign keys of B,C,D,E |
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jezemine
Master Smack Fu Yak Hacker
2886 Posts |
Posted - 2008-09-19 : 13:34:57
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how about you post the DDL for the tables, and the DML for query?
elsasoft.org |
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visakh16
Very Important crosS Applying yaK Herder
52326 Posts |
Posted - 2008-09-20 : 02:07:18
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quote:
Originally posted by sqlclarify
A contains the foreign keys of B,C,D,E
then you should be using the latter one |
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sqlclarify
Yak Posting Veteran
56 Posts |
Posted - 2008-09-20 : 21:47:25
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| Why should we use the latter one? What difference does it make?Could you please explain the reasoning?I am new to databases so I would like to know why this makes a difference.Thank you! |
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TG
Master Smack Fu Yak Hacker
6065 Posts |
Posted - 2008-09-20 : 23:13:22
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Assuming they are all INNER JOINs (on the same columns with either method) then I don't believe the results will be different. Depending on the indexes, the optimizer may come up with a better plan one way or the other. You can always compare the results from both methods to see for yourself.  Be One with the OptimizerTG |
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visakh16
Very Important crosS Applying yaK Herder
52326 Posts |
Posted - 2008-09-21 : 01:31:03
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quote:
Originally posted by sqlclarify
Why should we use the latter one? What difference does it make?Could you please explain the reasoning?I am new to databases so I would like to know why this makes a difference.Thank you!
i told use latter one since you've specified A contains foreign keys of B,C,D & E. So the relationship will be A->B,A->C,A->D & A->E |
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joining tables?