Adding index column in ADF Power Query

I read somewhere someone mention to transform the table into a list (perhaps this function https://learn.microsoft.com/en-us/powerquery-m/table-tolist), and then merge it with the list of numbers you have made (perhaps this function https://learn.microsoft.com/en-us/powerquery-m/list-zip).

And after that convert the resulting combined list into a table again.

I also think you can get great help with Power Query over at the Microsoft Power BI forum (this is the Microsoft Fabric Dataflows Gen2 forum).

https://community.fabric.microsoft.com/t5/Power-Query/bd-p/power-bi-services

Heavily inspired by Re: Adding index column in ADF Power Query - Microsoft Fabric Community:

let
    MyTable = Table.FromRecords({
        [Name="Alice", Age="30", Country="USA"],
        [Name="Bob", Age=null, Country="UK"],
        [Name="Charlie", Age="35", Country=null]
    },
    
    type table[Name = Text.Type, Age = Text.Type, Country = Text.Type]
    ),
    IndexList = List.Numbers(1, Table.RowCount(MyTable)),
    TableFromColumns = Table.FromColumns({MyTable[Name], MyTable[Age], MyTable[Country], IndexList}, type table[Name = Text.Type, Age = Int64.Type, Country = Text.Type, Index = Int64.Type])
in
    TableFromColumns

or

let
    MyTable = Table.FromRecords({
        [Name="Alice", Age="30", Country="USA"],
        [Name="Bob", Age=null, Country="UK"],
        [Name="Charlie", Age="35", Country=null]
    }),
    IndexList = List.Numbers(1, Table.RowCount(MyTable)),
    TableFromColumns = Table.FromColumns(Table.ToColumns(MyTable) & {IndexList}, Table.ColumnNames(MyTable) & {"Index"})
in
    TableFromColumns

(this second alternative means you don't need to specify the selected column names from MyTable inside the TableFromColumns. Instead, you select the whole table.)

Heavily inspired by Power Query - Combine tables without Merging 🔗🧲 (youtube.com):

(Also with this alternative, you don't need to specify the column names when combining the two tables.)

let
    MyTable = Table.FromRecords({
        [Name="Alice", Age="30", Country="USA"],
        [Name="Bob", Age=null, Country="UK"],
        [Name="Charlie", Age="35", Country=null]
    }
    ),
    IndexList = List.Numbers(1, Table.RowCount(MyTable)),
    IndexListAsTable = Table.FromList(IndexList, Splitter.SplitByNothing(), {"Index"}, null, ExtraValues.Error),
    TableToColumns = Table.PromoteHeaders(Table.FromColumns(Table.ToColumns(Table.DemoteHeaders(MyTable)) & Table.ToColumns(Table.DemoteHeaders(IndexListAsTable))))
in
    TableToColumns

Heavily inspired by Solved: Re: Merge tables without a join, placing new colum... - Microsoft Fabric Community:

(This uses quite different functions from the previous examples.
Also, you don't need to specify the column names when combining the two tables.)

let
    MyTable = Table.FromRecords({
        [Name="Alice", Age="30", Country="USA"],
        [Name="Bob", Age=null, Country="UK"],
        [Name="Charlie", Age="35", Country=null]
    }
    ),
    MyTableTransposed = Table.Transpose(Table.DemoteHeaders(MyTable)),
    IndexList = List.Numbers(1, Table.RowCount(MyTable)),
    IndexListAsTable = Table.FromList(IndexList, Splitter.SplitByNothing(), {"Index"}, null, ExtraValues.Error),
    IndexTransposed = Table.Transpose(Table.DemoteHeaders(IndexListAsTable)),
    AppendTables = Table.Combine({MyTableTransposed, IndexTransposed}),
    TransposeAppendedTables = Table.Transpose(AppendTables),
    #"Promoted Headers" = Table.PromoteHeaders(TransposeAppendedTables, [PromoteAllScalars=true]),
    #"Changed Type" = Table.TransformColumnTypes(#"Promoted Headers",{{"Name", type text}, {"Age", Int64.Type}, {"Country", type text}, {"Index", Int64.Type}})
in
    #"Changed Type"

These seem like interesting ways to just add a column to a table in Power Query without using a join condition.

I haven't checked if any of these will work in ADF Power Query, though.