Update Worksheet by comparing it to another Worksheet - vba

Question

I have an excel Worksheet ("Sheet1") that I need to compare with another Worksheet ("Sheet2").
Both Worksheets are formatted exactly alike. (i.e. columns are the same, with the same headers)
When comparing Sheet1 with Sheet2, I need to check for updates to existing records.
Also check for new records in Sheet2 that don't exist in Sheet1, and append them to the bottom of Sheet1.
Some Columns in Sheet 2 are completely blank and don't need to be checked.
Column 2 would be the "Key"
Also keep in mind that there are over 7000 rows in each worksheet.
Update #1:
Using the dictionary object, I came up with this. However, it doesn't seem to find any new entries. Am I doing something wrong?
Sub createDictionary()
Dim dict As Object
Set dict = CreateObject("Scripting.Dictionary")
Dim maxRows1, maxRows2 As Long
Dim i, j As Integer
Dim SheetOne, SheetTwo As Worksheet
maxRows1 = Sheets("Sheet1").UsedRange.Rows.Count
Set SheetOne = Sheet1
Set SheetTwo = Sheet2
For i = 2 To maxRows1
If Not dict.exists(SheetOne.Cells(i, 2).Value + " " + SheetOne.Cells(i, 11).Value) Then
dict.Add CStr(SheetOne.Cells(i, 2).Value) + " " + SheetOne.Cells(i, 11).Value, i
End If
Next i
maxRows2 = Sheets("Sheet2").UsedRange.Rows.Count
For j = 2 To maxRows2
If Not dict.exists(Sheet2.Cells(j, 2).Value) Then
SheetTwo.Range("A" & j & ":" & "Z" & j).Copy
SheetOne.Range("A" & maxRows1 + 1).Insert Shift:=xlDown
SheetOne.Range("A" & maxRows1 + 1).Interior.Color = RGB(200, 200, 200)
End If
Next j
Set dict = Nothing
End Sub

Answer 1

Try using a dictionary object, it doesn't have a limit on how much it can hold (only limit is your computer)
I would loop through sheet1, add each key to the dictionary and map it to a collection that stores the rowIndex and the hash made from the rows values. Then loop through the keys in sheet2 and see if each key exists in the dictionary; if it doesn't, copy the row to sheet1. If the key does exist, then hash the row in sheet2 and compare to the dictionary item, if they are different you know you need to update the row.
To copy a row and paste it really quickly, you can simply access a ow's value2 property. This will be useful when appending + when updating
Here's some test code to get you started.
Sub loopCellInColumn()
Dim cell As Object
Dim sheet As Worksheet
Dim rng As Range
Set sheet = ActiveSheet
Set rng = sheet.UsedRange.Columns("A").Cells
For Each cell In rng
Row = cell.Row
cell.Value = "Hello World" & Row
Next cell
End Sub
and for using a dictionary:
Sub createDictionary()
Dim dict As Object
Dim value As Collection
Set dict = CreateObject("Scripting.Dictionary")
Key = "hello"
Set value = New Collection
value.Add 100, "row"
value.Add "A2D121E4", "hash"
dict.Add Key, value
MsgBox "key exists: " & dict.exists(Key) & vbNewLine & "value: " & dict(Key).Item("hash")
End Sub
copy + paste using value2:
Sub test()
ActiveSheet.Rows(1).Value2 = ActiveSheet.Rows(2).Value2
End Sub
ex of getting a row as string:
Sub getRowAsString()
Dim cell As Object
Dim sheet As Worksheet
Dim str As String
Dim arr() As Variant
Dim arr2() As Variant
Dim printCol As Integer
Set sheet = ActiveSheet
printCol = sheet.UsedRange.Columns.Count + 1
For Each cell In sheet.UsedRange.Rows
arr = cell.Value2
ReDim arr2(LBound(arr, 2) To UBound(arr, 2))
For i = LBound(arr, 2) To UBound(arr, 2)
arr2(i) = arr(1, i)
Next i
str = Join(arr2, ", ")
ActiveSheet.Cells(cell.Row, printCol).Value = str
Next cell
End Sub
Here is a post of getting a hash value from string, includes vba code:
All of the steps I listed have numerous posts supporting them, so resources won't be an issue

Answer 2

I repeat this often across this forum :), however, such operations are much more easy to handle using SQL.
I would either use Microsof Query (Excel Data->Get External Data->From Other sources->From Microsoft Query) OR I suggest using my SQL Add-In to Excel: http://blog.tkacprow.pl/?page_id=130
Seems like you need to need to use the JOIN operator to find the changes between Sheets 1 and 2. Then using a UNION operator you join a second SELECT with a LEFT OUTER JOIN to add the additional new rows.