it's more a db2 question then a cobol question.
Cursor vs single select : If you're select returns more than one row (and you need those rows), you'll have to use a cursor.
If you only need the first one (but you're not allowed to "order by") you could use a single select with "fetch first 1 row only".
Multi-row fetching is more performant then single row fetching,but it complicates your program a bit.
Once you have a decent skeleton or example program its easy.
If you expect to do more then 1000 fetches, i would advise to certainly switch to multi-row.
But even for smaller cursors : once you're used to it : always use it.
if you google "multi-row fetch" you'll find all kind of interesting articles.
one being : http://it.toolbox.com/blogs/db2zos/why- ... cool-12229
I can explain it to you, but i can not understand it for you.