|Something is still not clear to me.|
"The reason I want VBA because new good ref # could come in anyway and it is nice to automate this."
A new good ref # could "come into" where? Main or Sheet2?
Where in the sheet would it "come into"? At the end of Column A? As a replacement for an existing ref #? Someplace else?
"Additionally, there is no any other column in the spreadsheet 2, it is simply included only ref #. "
I don't see why that matters. VLOOKUP only needs one column. Based on your example data, if you want to see which ref #'s in Main Column A also appear in Sheet2 Column A, use this in Main!C1 and drag it down:
=IF(ISNA(VLOOKUP(A1,Sheet2!$A:$A,1,0)),"Take A Look","Good")
Based solely on your example data, you should get this in Main:
A B C
1 5964 02/02/12 Take A Look
2 6588 02/02/12 Take A Look
3 1285 12/12/12 Good
I'm not saying that VBA is a bad idea; I just haven't seen any reason why you would want to use it in this case. If the VLOOKUP isn't "automatic" enough, please explain why.
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