Cemal,

>SELECT SUBSTR(partno,ATC("-",partno,1)+1,ATC("-",partno,2)-ATC("-",partno,1)-1) from plan
>
>Its returns
>ABC
>QWE

The width of the column established by the SQL SELECT is being determined by the calculation of the first record. Try adding a PADR around the expression:

SELECT <b>PADR(</b> SUBSTR(partno,ATC("-",partno,1)+1, ;
  ATC("-",partno,2)-ATC("-",partno,1)-1) <b>,15)</b> from plan