Select multiple rows with the same value(s)

Question

I have a table, sort of like this:

ID  |  Chromosome | Locus | Symbol | Dominance |
===============================================
1   |      10     |   2           


        

Answer 1

One way of doing this is via an exists clause:

select * from genes g
where exists
(select null from genes g1
 where g.locus = g1.locus and g.chromosome = g1.chromosome and g.id <> g1.id)

Alternatively, in MySQL you can get a summary of all matching ids with a single table access, using group_concat:

select group_concat(id) matching_ids, chromosome, locus 
from genes
group by chromosome, locus
having count(*) > 1