joinAlgorithm and keyEqualityComparers

Now I feel really honoured - thank you guys :-)

Honestly: I haven't recognized these 2 parameters before. And while the MS-documentation holds some things about the joinAlgorithms in here: https://msdn.microsoft.com/en-us/library/mt296614.aspx, there's zero about keyEqualityComparers.

But with regards to the desired relative comparison here (< or >), I dare to say that they probably wouldn't help, as M distinguishes between equality and relational comparisons.

So in order to not let you down here, please have a look at the following query, which performs a relative lookup (and will hopefully appeal to you DAX-masters :-) ):

let
    Table1 = #table({"Key1"},{{10},{20},{30},{40}}),
    Table2 = #table({"Key2"},{{9},{19},{29},{39}}),
    RelativeMerge = Table.AddColumn(Table1, "RelativeJoin", 
            (Earlier) => Table.SelectRows(Table2, 
                         each [Key2]<Earlier[Key1])),
    #"Expanded RelativeJoin" = Table.ExpandTableColumn(RelativeMerge, "RelativeJoin", {"Key2"}, {"Key2"})
in
    #"Expanded RelativeJoin"

(This is nested row-context: Yes, we have evaluation context in M as well & fortunately it doesn't behave like a moving target :-) )