Help me validate an AlphaNumeric Text column with specific rules/pattern

[BTATA]

I have student data from several sources that I can merge into a single table. 

Some sources are better at maintaining their data than others, and I'd like to "validate" a column if possible. 

Students in the UK have a 13-digit unique pupil number. This is made up of 1 letter at the start, followed by 12 numerical digits. 

I wanted to add a custom column in my PowerBI table which can return either a "Yes" or "No" (if the UPN matches the aforementioned rule - 1 letter, 12 digits).

For some reason, PowerBI doesn't like the following query...

= Table.AddColumn(#"Changed Type1", "UPN Validated", each IF(AND(NOT(ISNUMBER(LEFT([#"Unique Identifier*"], 1))),ISNUMBER(RIGHT([#"Unique Identifier*"], 12))), "Yes", "No"))

Can someone please help me figure out what's wrong with this formula? 

[Vijay_A_Verma · Accepted solution]

Use this

= Table.AddColumn(#"Changed Type1", "UPN Validated", each [First = Character.ToNumber(Text.Start([Unique Identifier], 1)), Last = Text.End([Unique Identifier], 12), a = First > 64 and First < 91, b = Value.FromText(Last) is number and Text.Length(Last) = 12, result = if (a and b) then "Yes" else "No"][result])

See the sample test code

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("JYy7DcAgEMV2oU7xuM+7oyQZA1GyQJT9lSh0lmV5jNJDMtBcQUWZxygfpdCyVfAXp2jCNFhpspM0UNRr0PtuFGqB9IBvUb8JPfWi7c39rGeVOV8=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Unique Identifier" = _t]),
    #"Added Custom" = Table.AddColumn(Source, "UPN Validated", each [First = Character.ToNumber(Text.Start([Unique Identifier], 1)), Last = Text.End([Unique Identifier], 12), a = First > 64 and First < 91, b = Value.FromText(Last) is number and Text.Length(Last) = 12, result = if (a and b) then "Yes" else "No"][result])
in
    #"Added Custom"

[BTATA]

Thank you so much Vijay! 

That worked perfectly 🙂