Highlight duplicates across a workbook

Question

I am trying to highlight duplicates across a workbook of 12 sheets.

We track ID#s and I want to highlight the cell if an ID# (value) is on any of the other sheets.

Answer 1

What this code does is loops through the values of Col A in the sheet which gets activated and then it searches the Col A of all the remaining worksheets and if it finds the ID then it colors the cell background to red.

TRIED AND TESTED

I have commented the code so you shouldn't have a problem understanding it. If you still do then simply post back :)

Try this

Private Sub Workbook_SheetActivate(ByVal Sh As Object)
    Dim lRow As Long, wsLRow As Long, i As Long
    Dim aCell As Range
    Dim ws As Worksheet
    Dim strSearch As String

    With Sh
        '~~> Get last row in Col A of the sheet
        '~~> which got activated
        lRow = .Range("A" & .Rows.Count).End(xlUp).Row

        '~~> Remove existing Color from the column
        '~~> This is to cater for any deletions in the
        '~~> other sheets so that cells can be re-colored
        .Columns(1).Interior.ColorIndex = xlNone

        '~~> Loop through the cells of the sheet which
        '~~> got activated
        For i = 1 To lRow
            '~~> Store the ID in a variable
            strSearch = .Range("A" & i).Value

            '~~> loop through the worksheets in the workbook
            For Each ws In ThisWorkbook.Worksheets
                '~~> This is to ensure that it doesn't
                '~~> search itself
                If ws.Name <> Sh.Name Then
                    '~~> Get last row in Col A of the sheet
                    wsLRow = ws.Range("A" & ws.Rows.Count).End(xlUp).Row

                    '~~> Use .Find to quick check for the duplicate
                    Set aCell = ws.Range("A1:A" & wsLRow).Find(What:=strSearch, _
                                                               LookIn:=xlValues, _
                                                               LookAt:=xlWhole, _
                                                               SearchOrder:=xlByRows, _
                                                               SearchDirection:=xlNext, _
                                                               MatchCase:=False, _
                                                               SearchFormat:=False)

                    '~~> If found then color the cell red and exit the loop
                    '~~> No point searching rest of the sheets
                    If Not aCell Is Nothing Then
                        Sh.Range("A" & i).Interior.ColorIndex = 3
                        Exit For
                    End If
                End If
            Next ws
        Next i
    End With
End Sub