Max Wanadoo
max.wanadoo at gmail.com
Mon Sep 21 17:04:56 CDT 2009
Are you saying that the FIRST JohnColby record you encounter is therefore the MASTER and the rest JohnColby record's data gets to update the MASTER? So, Rec 1. John Colby likes Fish (at the time he might have liked fish) Rec 2. John Colby does not like fish (might have been asked some time later, after a bad meal) Which takes precedence? Do you NOT overwrite existing data. Or DO you ? Max -----Original Message----- From: dba-vb-bounces at databaseadvisors.com [mailto:dba-vb-bounces at databaseadvisors.com] On Behalf Of jwcolby Sent: 21 September 2009 22:55 To: dwaters at usinternet.com; Discussion concerning Visual Basic and related programming issues. Subject: Re: [dba-VB] Merge rows Dan, In fact there are 50 million records in the table (though not that many "duplicates") so there is no "making a decision". Basically I have to take row one and update it with row 2, 3, 4... Delete row 2,3,4... This is basically a table of "polls" that people have taken, with ~600 fields where there may or may not be information about doing, wanting or having that thing. Everything from information about the boat you own to the electronics you own, to the medicine you take, whether you own a dog or cat, hunt, fish etc. In order to get in the database you have to have volunteered the information somewhere along the line. But you might have taken several different polls at different times. Thus one record might have the electronics you own, another the medicine you take, and you don't even own a boat so those fields contain nothing. Like that. I just want to take all the John Colby records and merge them into a single John Colby record, deleting all the extras when I am done. Of course this is one reason for my other question about getting rid of any fields where there is no information in any record. If I am going to process 50 million records, it would be good to not have to process any fields where there is no info to merge. The other reason for the other question is that doing a table scan against 50 million records with 640 fields is just plain going to take longer than a table scan against 50 million records with only 400 fields. It comes down to a matter of disk sectors to load. And with 640 fields you cannot have indexes against all of them, so you are going to be doing table scans. I just did a test where I did a Count() where... on a non-indexed field and it took 1:18. So just doing these counts on all 640 fields could take awhile. I will be counting and logging the count in my data dictionary table. And off we go... John W. Colby www.ColbyConsulting.com Dan Waters wrote: > This is a tough question - not technically difficult but what's tough is > actually making the choice! > > I think you'll need to get some guidance from your customer as to which > single record to keep (the latest one?), or should you put the contents of > all the related cells into one cell and delete the other rows? Or something > else? > > This probably doesn't help . . . > Dan _______________________________________________ dba-VB mailing list dba-VB at databaseadvisors.com http://databaseadvisors.com/mailman/listinfo/dba-vb http://www.databaseadvisors.com