Compare two column from two different sheets - excel

Question

I need to compare two columns in different worksheets.
First sheet (WITH 500 ROWS)
ColumnA(NUMBER) ColumnB(STRING) ColumnC(NUMBER)ColumnD(NUMBER)ColumnE(NUMBER)ColumnF(NUMBER)
Second Sheet
ColumnA(NUMBER) ColumnB(STRING) ColumnC(NUMBER)ColumnD(NUMBER)ColumnE(NUMBER)
with out ColumnF
I want to print out in sheet3 the SITESID(COLUMNA) from the second sheet that do not exist in the first sheet .
Option Explicit
Sub Compare()
Dim Row1Crnt As Long
Dim Row2Crnt As Long
Dim Row3Crnt As Long
Dim Row1Last As Long
Dim Row2Last As Long
Dim ValueSheet1
Dim ValueSheet2
Dim duplicate As Boolean
Dim maxColmn As Long
Dim i
maxColmn = 10 ' number of column to compare
For i = 1 To maxColmn
With Sheets("Sheet1")
Row1Last = .Cells(Rows.Count, i).End(xlUp).Row
End With
With Sheets("Sheet2")
Row2Last = .Cells(Rows.Count, i).End(xlUp).Row
End With
Row1Crnt = 2
Row2Crnt = 2
Row3Crnt = 2
maxColmn = 10
Do While Row2Crnt <= Row2Last
duplicate = False
Row1Crnt = 2
With Sheets("Sheet2")
ValueSheet2 = .Cells(Row2Crnt, i).Value
End With
Do While Row1Crnt <= Row1Last
With Sheets("Sheet1")
ValueSheet1 = .Cells(Row1Crnt, i).Value
End With
If ValueSheet1 = ValueSheet2 Then
duplicate = True
Exit Do
End If
Row1Crnt = Row1Crnt + 1
Loop
If duplicate = False Then
With Sheets("Sheet3")
.Cells(Row3Crnt, i).Value = ValueSheet2
Row3Crnt = Row3Crnt + 1
End With
End If
Row2Crnt = Row2Crnt + 1
Loop
Next
End Sub
But I'll take that as a result
all columnA (SITESID) sheet2 and ColumnB(NAMES) from the second sheet that do not exist in the first sheet

Answer 1

The quickest 'check for exist' is application.match.
sub compare
dim a as long, arr as variant, chk as variant
with worksheets("sheet1")
arr = .range(.cells(2, "A"), .cells(.rows.count, "A").end(xlup)).value2
end with
with worksheets("sheet3")
for a = lbound(arr, 1) to ubound(arr, 1)
if iserror(application.match(arr(a, 1), worksheets("sheet2").columns("A"), 0)) then
.cells(.rows.count, "A").end(xlup).offset(1, 0) = arr(a, 1)
end if
next a
end with
end sub