Interesting Variation Of Duplicate Check Help Please

Good morning all,

I have been tasked with an interesting problem using SQL 2005. Simplified it looks like this: I have two tables both well over a million rows, totalling unrelated keys between the tables. I need to find records in table one that do not exist in table two, the twist is this, I need to find rows where the invoice number in table 1 does not exist at all in table 2 or where the invoice number exists but the timestamp associated with the invoice in table 2 is more than 10secs different than the invoice/timestamp in table 1. I'm fairly new to sql and, although I can do the really simple stuff, this one is over my head I'm afraid. Any help at all would be greatly appreciated. I would also like to hear any suggestions regarding books that might give examples of sql code at around this level of difficulty. Thanks in advance for your assistance! Paul