help for sql language

Hi all, please help my concern to using SQL language. My database stored 2~4 million record in one table a day and all redords are stored in time basis which has start and end time fields in day table, of course it has other information in the same record. In above, I need to unload information to file from database and I'm using SQL sentence as belows. ....... isql xxx@yyy_tcp << EOF unload to $outdir/zzz.txt select * from $table where id = "70" and etime >= "$stm;EOF As I mentioned, all information stored in time sequende which is 00:00:00 ~ 23:00:00 order and I unload files ever 30 minutes to makes 48 file a day. However, I have some trouble in the afternoon because isql search information from the start postion in table which takes time to collect recent information. So, I'd like ask anyone to collect information in reverse order from the table in sql language. your information will reduce my pain at this stage. Sincerely