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Re: Joining two tables using *two* columns (instead of one)

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On 04/05/2012 03:21 PM, Mateusz wrote:
> Hi,
> 
> I'm stuck with a (maybe simple) problem of JOINing two tables.. The thing is that I need to join these tables on two different columns.
> 
> Let's say I have a table called "subnet" with three columns: id, probe1, probe2. probe1 and probe2 are both foreign keys to a 'probes' table that contains columns: id, value. Now, I 
> need to join all this together...
> 
> This is what I tried so far:
> 
> SELECT id, prob1.value AS p1, prob2.value AS p2
>   FROM subnet
>   LEFT OUTER JOIN probes AS prob1 ON prob1.id=probe1
>   LEFT OUTER JOIN probes AS prob2 ON prob2.id=probe2
>   WHERE probe1 IS NOT NULL AND probe2 IS NOT NULL;

Without giving it to much thought, this should be equal with:

SELECT id, prob1.value AS p1, prob2.value AS p2
FROM subnet
JOIN probes AS prob1
    ON  prob1.id=probe1
JOIN probes AS prob2
    ON prob2.id=probe2;

With proper indexes there's a good chance that this will be less
resource demanding


/Lennart

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Thread

Joining two tables using *two* columns (instead of one) Mateusz <no@spam.please> - 2012-04-05 15:21 +0200
  Re: Joining two tables using *two* columns (instead of one) Lennart Jonsson <erik.lennart.jonsson@gmail.com> - 2012-04-05 16:30 +0200
    Re: Joining two tables using *two* columns (instead of one) Mateusz <no@spam.please> - 2012-04-05 18:01 +0200
      Re: Joining two tables using *two* columns (instead of one) Robert Klemme <shortcutter@googlemail.com> - 2012-04-05 23:16 +0200
        Re: Joining two tables using *two* columns (instead of one) Mladen Gogala <gogala.mladen@gmail.com> - 2012-04-06 01:00 +0000
          Re: Joining two tables using *two* columns (instead of one) Jasen Betts <jasen@xnet.co.nz> - 2012-04-06 04:12 +0000
            Re: Joining two tables using *two* columns (instead of one) Mladen Gogala <gogala.mladen@gmail.com> - 2012-04-06 04:44 +0000
              Re: Joining two tables using *two* columns (instead of one) Robert Klemme <shortcutter@googlemail.com> - 2012-04-06 14:17 +0200
                Re: Joining two tables using *two* columns (instead of one) Mladen Gogala <gogala.mladen@gmail.com> - 2012-04-08 19:01 +0000
    Re: Joining two tables using *two* columns (instead of one) Jasen Betts <jasen@xnet.co.nz> - 2012-04-05 21:20 +0000
      Re: Joining two tables using *two* columns (instead of one) Lennart Jonsson <erik.lennart.jonsson@gmail.com> - 2012-04-06 09:30 +0200
        Re: Joining two tables using *two* columns (instead of one) Jasen Betts <jasen@xnet.co.nz> - 2012-04-06 23:42 +0000
        Re: Joining two tables using *two* columns (instead of one) Lennart Jonsson <erik.lennart.jonsson@gmail.com> - 2012-04-08 20:39 +0200
  Re: Joining two tables using *two* columns (instead of one) Mladen Gogala <gogala.mladen@gmail.com> - 2012-04-05 19:48 +0000
    Re: Joining two tables using *two* columns (instead of one) Mladen Gogala <gogala.mladen@gmail.com> - 2012-04-05 19:50 +0000
    Re: Joining two tables using *two* columns (instead of one) Mateusz <no@spam.please> - 2012-04-06 09:13 +0200
  Re: Joining two tables using *two* columns (instead of one) Jasen Betts <jasen@xnet.co.nz> - 2012-04-05 21:28 +0000
    Re: Joining two tables using *two* columns (instead of one) Mateusz <no@spam.please> - 2012-04-06 09:00 +0200
      Re: Joining two tables using *two* columns (instead of one) Jasen Betts <jasen@xnet.co.nz> - 2012-04-06 23:38 +0000
  Re: Joining two tables using *two* columns (instead of one) Mateusz <no@spam.please> - 2012-04-06 08:48 +0200
    Re: Joining two tables using *two* columns (instead of one) Robert Klemme <shortcutter@googlemail.com> - 2012-04-06 14:33 +0200
      Re: Joining two tables using *two* columns (instead of one) Mladen Gogala <gogala.mladen@gmail.com> - 2012-04-11 03:21 +0000
    Re: Joining two tables using *two* columns (instead of one) Torsten Kirschner <torsten.kirschner@gmail.com> - 2012-04-10 05:58 +0200
      Re: Joining two tables using *two* columns (instead of one) Fredrik Jonson <fredrik@jonson.org> - 2012-04-10 08:53 +0000
        Re: Joining two tables using *two* columns (instead of one) Torsten Kirschner <torsten.kirschner@gmail.com> - 2012-04-11 00:06 +0200
          Re: Joining two tables using *two* columns (instead of one) Robert Klemme <shortcutter@googlemail.com> - 2012-04-12 20:38 +0200

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