For WRKQRY, WRKQMQRY and SQL, using the default key defined in the DDS for a LF may not be the optimal situation when running a query. In your case if you are using just 1 file, it may make sense but you could be joining multiple files. Without a sort it will optimize the returned data. If no sort / order by was defined in the query or SQL the system decides the best sequence. Defining keys can be a big help with performance. We had one query that ran for 10-12 minutes. There was a join to a file with around 14 million records. We created a LF with the 6 keys matching our join and then used this file new LF and the query now takes about 15 seconds.