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POEfficient SQL to calculate # of shared affiliations
 

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  1. POEfficient SQL to calculate # of shared affiliations
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    <p>So I have </p> <ol> <li>a table that stores asymmetrical connections between two persons (like a Twitter follow; <em>not</em> like a Facebook friend) and </li> <li>a table that stores a person's affiliations to various groups</li> </ol> <p>My task is to find, for each asymmetrical relationship, the number of affiliations shared between the "from person" and the "to person".</p> <p>I made this brute force solution, but I'm wondering if brighter minds could come up with something more efficient.</p> <pre><code>select frm01.from_person_id, frm01.to_person_id, count(*) num_affl from ( select lnk.from_person_id, lnk.to_person_id, ga.grp_id from_grp_id from links lnk left outer join grp_affl ga on lnk.from_person_id = ga.person_id group by lnk.from_person_id, lnk.to_person_id, grp_id ) frm01 inner join ( select lnk.from_person_id, lnk.to_person_id, ga.grp_id to_grp_id from links lnk left outer join grp_affl ga on lnk.to_person_id = ga.person_id group by lnk.from_person_id, lnk.to_person_id, grp_id ) to01 on ( frm01.from_person_id = to01.from_person_id and frm01.to_person_id = to01.to_person_id and frm01.from_grp_id = to01.to_grp_id ) group by frm01.from_person_id, frm01.to_person_id; </code></pre> <p>Using ANSI SQL on Netezza (which doesn't allow correlated subqueries).</p> <p>TIA!</p> <p>Edited to add table schema:</p> <pre><code>table lnk: from_person_id to_person_id 1 4 2 5 3 6 4 2 5 3 table grp_affl: person_id grp_id 1 A 1 B 1 C 2 A 3 B 4 C 5 A 5 B 5 C 6 A expected output: from_person_id to_person_id num_affl 1 4 1 2 5 1 3 6 0 4 2 0 5 3 1 </code></pre> <p>Persons 1 &amp; 4 have 1 affiliation in common (C), 2 &amp; 5 have A in common, 5 &amp; 3 have B in common. 3 &amp; 6 have nothing in common. Likewise 4 &amp; 2.</p>
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    1. USSQLCurious
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    1. COI'd always recommend to post the table schema and if you have sample data and your expected output then that would help a lot.
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      1. USMosty Mostacho
 

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