I have a big fat query that's written dynamically to integrate some data. Basically what it does is query some tables, join some other ones, treat some data, and then insert it into a final table.

The problem is that there's too much data, and we can't really trust the sources, because there could be some errored or inconsistent data.

For example, I've spent almost an hour looking for an error while developing using a customer's database because somewhere in the middle of my big fat query there was an error converting some varchar to datetime. It turned out to be that they had some sales dating '2009-02-29', an out-of-range date. And yes, I know. Why was that stored as varchar? Well, the source database has 3 columns for dates, 'Month', 'Day' and 'Year'. I have no idea why it's like that, but still, it is.

But how the hell would I treat that, if the source is not trustable?

I can't HANDLE exceptions, I really need that it comes up to another level with the original message, but I wanted to provide some more info, so that the user could at least try to solve it before calling us.

So I thought about displaying to the user the row number, or some ID that would at least give him some idea of what record he'd have to correct. That's also a hard job because there will be times when the integration will run up to 80000 records. And in an 80000 records integration, a single dummy error message: 'The conversion of a varchar data type to a datetime data type resulted in an out-of-range datetime value' means nothing at all.

So any idea would be appreciated.

Oh I'm using SQL Server 2005 with Service Pack 3.