Finding the Previous Invoice's Post Date

Hi afat_aliyev - I would use Power Query in this scenario.  If you add add 2 Index columns to the table.  The first starts a 1 and the second starts at 0.  The table can be joined to itself on the Index columns.  Use expand columns to get the additional column with the previous date.  The following script shows an example of this:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjAwMFTSUTI00Dc20DcyMDJQitUBixqBRA31jcxRRI1Bokb6RqZQ0VgA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [InvoiceNumber = _t, PostDate = _t]),
    #"Parsed Date" = Table.TransformColumns(Source,{{"PostDate", each Date.FromText(_, "en-US"), type date}}),
    #"Added Index" = Table.AddIndexColumn(#"Parsed Date", "Index - 1", 1, 1, Int64.Type),
    #"Added Index1" = Table.AddIndexColumn(#"Added Index", "Index", 0, 1, Int64.Type),
    #"Merged Queries" = Table.NestedJoin(#"Added Index1", {"Index"}, #"Added Index1", {"Index - 1"}, "Added Index1", JoinKind.LeftOuter),
    #"Expanded Added Index1" = Table.ExpandTableColumn(#"Merged Queries", "Added Index1", {"PostDate"}, {"Previous Post Date"}),
    #"Removed Columns" = Table.RemoveColumns(#"Expanded Added Index1",{"Index - 1", "Index"}),
    #"Sorted Rows" = Table.Sort(#"Removed Columns",{{"InvoiceNumber", Order.Ascending}})
in
    #"Sorted Rows"