Transform Column / Type

Hi Dicken 

I think it's the behavior of Table.TransformColumns. If you see 

Table.TransformColumns - Table Function | Power Query M

this function decides how to apply the transformation function to each value or whether to update the column type metadata.

In { "Date", each Date.From(_) }, Table.TransformColumns only sees a custom lambda, “(x) => Date.From(x)”. It doesn’t know the return type of this lambda, so it leaves the column type metadata unchanged.

While in { "Date", Date.From }, Table.TransformColumns sees a native function that has a declared return type in the M library (type date). Since it knows that return type, it sets the column’s metadata to date as well.

Ran a simple test below, 

let
    Query1 = 
  let
    Source = #table(type table [Date = text], {{"2025-08-22"}}),
    Transform1 = Table.TransformColumns(Source, {"Date", each Date.From(_)}),
    Transform2 = Table.TransformColumns(Source, {"Date", Date.From})
  in
    { Transform1, Transform2 }
in
    Query1