Auto copy formula from a cell, to other cells when adjacent cell on row contains data?

[helpneeded2]

I am trying to create a spreadsheet that will be used by multiple people in which data from a an SQL pull will be pasted into the sheet. This data may vary from 100 rows of data to 20,000 rows.

For best sheet performance I would like to avoid having a formula in 20,000 rows that tests whether there is data in each of the rows, and outputs a value if there is data. My sheet has several similar data tabs, and when I placed in the formula down the 20,000 rows on each tab, the sheet size increased 10-fold and the time to calculate is now measured in minutes.

Although I have had very minimal exposure to VBA, I would like to have a script that would copy a formula from the first row (adjacent to existing data), and paste it down the column for every other adjacent row with data.

To help simplify what I am trying to do, here is an example:

	A	B	C	D
1	22	23	=A1+B1
2	44	23
3	2343	339
4

In the above example, I want any formula in C1 to be copied down to the last row in Column C in which data exists in Column A.

While looking at examples from a browser search, I think the most accurate VBA I found was this:

Sub test()
Dim lastrow As Long
    lastrow = Range("A" & Rows.Count).End(xlUp).Row
    Range("C1").AutoFill Destination:=Range("C2:C" & lastrow), Type:=xlFillDefault
End Sub

However when I try to run this I get an error. (Run-time error '1004': AutoFill method of Range class failed)

Could someone please post a suggestion on how I could do this.

Thank you.

 

[Fluff]

As your question is signifcantly different from the op, you need to start a new thread. Thanks