If statement

This will work:

= Table.Combine({#"Table A", Table.SelectRows(#"Table B", each not List.Contains(List.Buffer(#"Table A"[Job NO]), [Job NO]))})

--Nate

Hello Anonymous 

I would suggest you to use a Join, applying LeftAnti. Here an example

let
    A = 
    let
        Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMlTSAeJYnWglIyDLCMwyBrKMlWJjAQ==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Job NO" = _t, Cost = _t]),
        #"Changed Type" = Table.TransformColumnTypes(Source,{{"Job NO", Int64.Type}, {"Cost", Int64.Type}})
    in
        #"Changed Type",
    B = 
    let
        Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMlTSAeJYnWglIyDLCMwyA7KMwSxzIMtEKTYWAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Job NO" = _t, Cost = _t]),
        #"Changed Type" = Table.TransformColumnTypes(Source,{{"Job NO", Int64.Type}, {"Cost", Int64.Type}})
    in
        #"Changed Type",
    
    AddTableBtoAUsingTableNestedJoin = Table.Combine
    (
        {
            A,
            Table.RemoveColumns
            (
                Table.NestedJoin
                (
                    B,
                    "Job NO",
                    A,
                    "Job NO",
                    "A",
                    JoinKind.LeftAnti
                ),
                {"A"}
            )
        }
    )
    
in
    AddTableBtoAUsingTableNestedJoin

Copy paste this code to the advanced editor in a new blank query to see how the solution works.

If this post helps or solves your problem, please mark it as solution (to help other users find useful content and to acknowledge the work of users that helped you)
Kudoes are nice too

Have fun

Jimmy