Start date and end date

Hello Rune_ 

group your data on you job-columns and add 3 functions.

One all rows, one min on Posting date and one max on Posting date. Afterwards expand your AllRows-Column

Here a example

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjTQMzDXMzIwtFDSAXIMzEG0gaFSrA5Qzhi3nIEleXJ47RsscrEA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Posting Date" = _t, #"Job No_" = _t, #"Job Task No_" = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Posting Date", type date}, {"Job No_", Int64.Type}, {"Job Task No_", Int64.Type}},"de-DE"),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"Job No_", "Job Task No_"}, {{"AllRows", each _, type table [Posting Date=date, Job No_=number, Job Task No_=number]}, {"Start Date", each List.Min([Posting Date]), type date}, {"End Date", each List.Max([Posting Date]), type date}}),
    #"Expanded AllRows" = Table.ExpandTableColumn(#"Grouped Rows", "AllRows", {"Posting Date"}, {"Posting Date"})
in
    #"Expanded AllRows"

Copy paste this code to the advanced editor in a new blank query to see how the solution works.

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Kudoes are nice too

Have fun

Jimmy