SQL Query with ODBC, Joins and Group Bys
You have a working query, but you are selecting:

FROM CF30, EC01, OC02, OM01U1, RS2101F 


With no explicit joins and only one implicit join:

WHERE OM01U1.OM01015 = RS2101F.OUTNUM


This is going to lead to problems. Can you find which fields (columns) match to which in each table? You could then say:

FROM OM01U1 
INNER JOIN RS2101F
ON OM01U1.OM01015 = RS2101F.OUTNUM


For example.

You may also find it useful to add a derived table:

SELECT OUTNUM, Max(RS2101F.DELDATE) FROM RS2101F


So that would then read:

FROM OM01U1 
INNER JOIN (
     SELECT OUTNUM, Max(RS2101F.DELDATE) 
     FROM RS2101F
     GROUP BY OUTNUM) As t
ON OM01U1.OM01015 = t.OUTNUM