how to write formula when doing query

Hi, Anonymous 

Based on your description, I created data to reproduce your scenario. The pbix file is attached in the end.

Table:

Here is the codes in 'Advanced Editor'.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("ZdK7CsMwDAXQXymeQ9EjfuQ/Ch1CMB0yNdChHfL5TVxZptagyQdf+eJ5dugGR8fwMfd1fVIGvtxen8d23bf37pZhLufnIChC6BFXFBuKPRoF0aiIxh55WYfEcAbqTRAzNTP1JorBoAhDj1INY0VkCpgEMShiU0Bp53xXjRszmDhEQciq0OQhiSJQRTaQq4pNmcrxFF7kiXwGUzl6QWW/n0I0KlSVmkpGRVHkVZE3KklTNTBksIGToNSQySsdlZu8KjR5hKKIVNH/t1q+", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Content = _t, Month = _t, Day = _t, Name = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Content", Int64.Type}, {"Month", Int64.Type}, {"Day", Int64.Type}, {"Name", type text}}),
    Custom1 = Table.SelectRows(#"Changed Type",each let d=[Day],m=Date.Month(DateTime.LocalNow()),n=[Month] in n=m or 
(
(m-n)=1 and
d=Record.Field( Table.Max(Table.SelectRows(#"Changed Type",each [Month]=n), "Day"),"Day")
)
 or
(
 (m-n)=2 and
 d=Record.Field( Table.Max(Table.SelectRows(#"Changed Type",each [Month]=n), "Day"),"Day")
 ) 
)
in
    Custom1

Result:

Best Regards

Allan

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