How to use M code create a column contain date and text

Hi, wangjuan303 ;

Try it.

= Table.AddColumn(#"Changed Type", "Custom", each if [Date] = List.Max(#"Changed Type"[Date]) then "Latest date" 
else if [Date] = List.Sort(#"Changed Type"[Date],Order.Descending){1} then "Previous date" else [Date])

The complete M language：

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjIwMjQAQiUdMFPXAISUYnWgMsYGpnAZY10gBy5jaWQEl7HUBXJgMoZGRnA9hka6QE5sLAA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [DateKEY = _t, Date = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"DateKEY", Int64.Type}, {"Date", type date}}),
    Custom1 = Table.AddColumn(#"Changed Type", "Custom", each if [Date] = List.Max(#"Changed Type"[Date]) then "Latest date" 
else if [Date] = List.Sort(#"Changed Type"[Date],Order.Descending){1} then "Previous date" else [Date])
in
    Custom1

The final output is shown below:

Best Regards,
Community Support Team_ Yalan Wu
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