Fill primary table using secondary table (join question)

Hi Anonymous ,

One sample for your reference, please check the following steps as below.

1. Add custom columns in both tables like this.

[Products]&[Severity]

2. Merge tables (LeftOuter) and fill the date column down.

M code for your reference.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WCijKTylNLlFwVNJRCk4tSy3KLKlUMFSK1cEhZYRbyhi3lAmKlBNuu5xw2+WE2y4nNLtiAQ==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type text) meta [Serialized.Text = true]) in type table [Products = _t, Severity = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Products", type text}, {"Severity", type text}}),
    #"Added Custom" = Table.AddColumn(#"Changed Type", "Custom", each [Products]&[Severity]),
    #"Merged Queries" = Table.NestedJoin(#"Added Custom", {"Custom"}, TableA, {"Custom"}, "TableA", JoinKind.LeftOuter),
    #"Expanded TableA" = Table.ExpandTableColumn(#"Merged Queries", "TableA", {"Products", "Date"}, {"TableA.Products", "TableA.Date"}),
    #"Filled Down" = Table.FillDown(#"Expanded TableA",{"TableA.Date"})
in
    #"Filled Down"

PBIX as attached.