Question

I have a database table structured like this (irrelevant fields omitted for brevity):

rankings
------------------
(PK) indicator_id
(PK) alternative_id
(PK) analysis_id
rank

All fields are integers; the first three (labeled “(PK)”) are a composite primary key. A given “analysis” has multiple “alternatives”, each of which will have a “rank” for each of many “indicators”.

I’m looking for an efficient way to compare an arbitrary number of analyses whose ranks for any alternative/indicator combination differ. So, for example, if we have this data:

analysis_id | alternative_id | indicator_id | rank
----------------------------------------------------
          1 |              1 |            1 |    4
          1 |              1 |            2 |    6
          1 |              2 |            1 |    3
          1 |              2 |            2 |    9
          2 |              1 |            1 |    4
          2 |              1 |            2 |    7
          2 |              2 |            1 |    4
          2 |              2 |            2 |    9

…then the ideal method would identify the following differences:

analysis_id | alternative_id | indicator_id | rank
----------------------------------------------------
          1 |              1 |            2 |    6
          2 |              1 |            2 |    7
          1 |              2 |            1 |    3
          2 |              2 |            1 |    4

I came up with a query that does what I want for 2 analysis IDs, but I’m having trouble generalizing it to find differences between an arbitrary number of analysis IDs (i.e. the user might want to compare 2, or 5, or 9, or whatever, and find any rows where at least one analysis differs from any of the others). My query is:

declare @analysisId1 int, @analysisId2 int;
select @analysisId1 = 1, @analysisId2 = 2;

select 
    r1.indicator_id, 
    r1.alternative_id,
    r1.[rank] as Analysis1Rank,
    r2.[rank] as Analysis2Rank
from rankings r1
inner join rankings r2
    on r1.indicator_id = r2.indicator_id
        and r1.alternative_id = r2.alternative_id
        and r2.analysis_id = @analysisId2
where
    r1.analysis_id = @analysisId1
    and r1.[rank] != r2.[rank]

(It puts the analysis values into additional fields instead of rows. I think either way would work.)

How can I generalize this query to handle many analysis ids? (Or, alternatively, come up with a different, better query to do the job?) I’m using SQL Server 2005, in case it matters.

If necessary, I can always pull all the data out of the table and look for differences in code, but a SQL solution would be preferable since often I’ll only care about a few rows out of thousands and there’s no point in transferring them all if I can avoid it. (However, if you have a compelling reason not to do this in SQL, say so–I’d consider that a good answer too!)

Answer 1

This will return your desired data set – Now you just need a way to pass the required analysis ids to the query. Or potentially just filter this data inside your application.

    select r.* from rankings r
    inner join
    (
        select alternative_id, indicator_id
        from rankings
        group by alternative_id, indicator_id
        having count(distinct rank) > 1
    ) differ on r.alternative_id = differ.alternative_id
    and r.indicator_id = differ.indicator_id
    order by r.alternative_id, r.indicator_id, r.analysis_id, r.rank