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sqloracle11g

SQL to compare two distinct group column different values in one table

Suppose one table t as following:

    c1 c2
    == ==
    a  1
    a  2
    b  1
    b  2
    b  3
    c  4
    c  2

We group this table by c1, and it has three groups: a, b, c. I need to calculate the similarity of column c2 between two groups, like the following:


    sim(a,b) = 2(common value of c2 are 1 and 2)/3(all value)=2/3
    sim(b,c) = 1(b and c has only one value 2 in common)/4 = 1/4
    sim(a,c) = 1/3

Can we use SQL (Oracle 11g syntax first) to construct the expression above?

Solution

  • I believe this query does what you want:

    select t1.c1, t2.c1, count(*) as NumInCommon,
       (select count(distinct t.c2)
        from t
        where t.c1 in (t1.c1, t2.c1)
       ) as NumInTotal
from t t1 join
     t t2
     on t1.c2 = t2.c2
group by t1.c1, t2.c1