Ludwig Kniprath napisal 24.10.2008 11:45:
Join-table
mn_2_r_id mn_2_c_id
1 1
1 2
1 3
1 4
2 1
3 2
3 5
4 3
...
(in real database this relation is an gis-relation with thousands of
rivers and countries, related by spatial join, but the problem is the
same...)
I want to know, which river is running through communities 1,2,3 *and* 4?
You can see the solution by just looking at the data above (only
"river_1" is running through all these countries), but how to query this
by sql?
select mn_2_r_id from join_table
where mn_2_c_id in (1,2,3,4)
group by mn_2_r_id having count(*)=4
(4 = how many communities we should find)
--
Regards,
Tomasz Myrta
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