Join Calender table with Main Table using 2 Date Columns

How would you want this to look? In your example Anonymous you show a Jan 1 2020 start date and a Jan 1, 9999 end date. What is the "single" date you need?

If you want a single date column, you can definitely do that. By adding this formula to a custom column you will get a list of values that can be converted to a date:

{Number.From([Start Date])..Number.From([End Date])}

But in your date examples, that will be over 2.7M records going out to the year 9999.

It would look like this. You would just remove start/end date and rename Date Range to your Date column to join to the calendar table with.

Full code here.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMtQ31DcyMDJQ0gEzLYFAKTYWAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Start Date" = _t, #"End Date" = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"End Date", type date}, {"Start Date", type date}}),
    #"Added Custom" = Table.AddColumn(#"Changed Type", "Date Range", each {Number.From([Start Date])..Number.From([End Date])}),
    #"Expanded Date Range" = Table.ExpandListColumn(#"Added Custom", "Date Range"),
    #"Changed Type1" = Table.TransformColumnTypes(#"Expanded Date Range",{{"Date Range", type date}})
in
    #"Changed Type1"

How to use M code provided in a blank query:
1) In Power Query, select New Source, then Blank Query
2) On the Home ribbon, select "Advanced Editor" button
3) Remove everything you see, then paste the M code I've given you in that box.
4) Press Done
5) See this article if you need help using this M code in your model.

If that isn't what you need, please be more speific on the expected output.

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