select
id, a, b
from your_table t
join (select a, b from your_table group by a, b having count(1) > 1) dup on dup.a = t.a and dup.b = t.b
select
id, a, b
from your_table t
join (select a, b from your_table group by a, b having count(1) > 1) dup on dup.a = t.a and dup.b = t.b
