Find if a date changes

Hi gmasta1129,
In case you'd like to do this query on Power Query. Here's a solution that you can refer to. Let me know in case there are any confusions. Thanks

Code:
let
Source = [SourceData],
Group = Table.Group(
Source,
{"facility code"},
{
{
"AllRows",
each
let
AddColumn = Table.AddIndexColumn(_, "Due Date?", 0, 1),
Transform = Table.TransformColumns(
AddColumn,
{
"Due Date?",
each try AddColumn[maturity date]{_ - 1} otherwise AddColumn[maturity date]{_}
}
),
DueColumn = Table.AddColumn(
Transform,
"Due Date",
each if [maturity date] = [#"Due Date?"] then "N" else "Y"
)
in
DueColumn
}
}
),
Combine = Table.Combine(Group[AllRows])
in
Combine

In Power Query, you can add an Index column to refer to the previous row.

Paste the below code into the Advanced Editor to see how it works:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjTQN9Q3MjAyVdJRMje0MDAG0mb6RuYgMXOlWB2wCiOCKowJqjAjqMIcU4WxAUjMAqbCgqAZlgRVGBrgURILAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Run Date" = _t, #"facility code" = _t, #"maturity date" = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Run Date", type date}, {"facility code", Int64.Type}, {"maturity date", type date}}),
    #"Added Index" = Table.AddIndexColumn(#"Changed Type", "Index", 0, 1, Int64.Type),
    #"Added Custom" = Table.AddColumn(#"Added Index", "Change?", each 
        if [Index] = 0 then "N" 
        else if #"Changed Type"[maturity date]{[Index]-1} = [maturity date] then "N" else "Y", type text)
in
    #"Added Custom"

gmasta1129  Try this:

let
    Source = Excel.CurrentWorkbook(){[ Name = "Table1" ]}[Content],
    ChangedType = Table.TransformColumnTypes (
        Source,
        { { "Run Date", type date }, { "facility code", Int64.Type }, { "maturity date", type date } }
    ),
    Recs = Table.ToRecords ( ChangedType ),
    Acc = List.Accumulate (
        List.Skip ( Recs ),
        { List.First ( Recs, 1 ) & [ Date Change = "N" ] },
        ( s, c ) =>
            s
                & {
                    if List.Last ( s )[#"maturity date"] <> c[#"maturity date"] then
                        c & [ Date Change = "Y" ]
                    else
                        c & [ Date Change = "N" ]
                }
    ),
    Result = Table.FromRecords (
        Acc,
        type table [ Run Date = date, facility code = Int64.Type, maturity date = date, Date Change = text ]
    )
in
    Result

Excel file attached below.

gmasta1129:
Thanks to ronrsnfld  and AntrikshSharma for their Power Query solutions—both work perfectly. For very large datasets, I’d recommend ronrsnfld's approach; it’s faster than AntrikshSharma ’s, because the latter transforms the object multiple times (Table → Record → Table). 

Add a calculated column:

gmasta1129

Hello ThxAlot ,

This worked perfectly. Thank you so much for your help. I appreciate it.