zOs/TX/PER18SEL

select a.k3, b.d9
    from tper18 a, tper18 b
    where a.k3 = b.d9 and a.k9 = 'xyzxyz'
;
select a.k9, b.d3
    from tper18 a, tper18 b
    where a.k9 = b.d3
;
select a.k9, b.d3
    from tper18 a, tper18 b
    WHERE CAST(A.K9 AS CHAR(3))=B.D3