select *
from link_table le
where le.link_site = '3' or le.linked_site ='3'
and not exists (select 0
from link_table li
where li.link_site = le.linked_site
and le.link_site = li.linked_site)
2009/12/18 Ease Bus <[email protected]>
> Please help me with finding a SQL select statement for the following
> problems.
>
> I have two classes: Site and Link
>
> Table Link has two columns: linking_site_id, and linked_site_id
>
> I would like to find all the links in table Link where linking_site_id
> = 3 or linked_site_id = 3 but only include a link where linked_site_id
> = 3 if the linking_site_id in that link is not one of the
> linked_site_id that site 3 links to. For example, if the Link table
> contains the following rows
>
> Linking_site Linked_site
> 2 1
> 3 2
> 3 4
> 5 3
> 2 3
>
> What SQL select statement would return only the following:
>
> 3 2
> 3 4
> 5 3
>
> If SQL query alone cannot do this, what is the most efficient way to
> do it via RoR? Thanks.
>
> Thanks.
>
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