Hi varior,
There are many different ways to do this and I believe it depends on the volume of data you'll be processing.
You could set up a tOracleInput for your Oracle connection and then a tFileDelimited for ORDER_NO_LIST.txt as a lookup into a tMap. Turn on inner join and you'll get the matches.
Second option is to pre-process ORDER_NO_LIST.txt using a tJavaRow/tPerlRow to create a string that looks like "123456,456789" and store it in global or context variable. Then do a OnSubJobOK connector to your tOracleInput where the query would look something like (in pseudocode):
"select * from ORDER where ORDER_NO IN (" + context.orderlistnostring + ")"
Either of these options will work.
Cheers,
c0utta