Allays return value from left table in join

I have 2 tables A and B

A has cols(AKey, val1, val2) B has Cols(BKey,Akey, ValX, valY)

i have the following query

    select a.Val1,a.Val2,b.ValX
    from A
    Left Join B on a.AKey = b.Akey
    where a.Akey ={someValue}
    and ((b.valY ={aDifferentVal}) or (b.valY is NULL))

The situation is that i always want to return the values from table A. and this works when {aDifferentVal} exists in the the join, it also works when there are no values in table B for the Join, However when there are values in table be for the Join but none of these are {aDifferentVal} then the query return nothing, and i still want the values from table A.

How can i achieve this?

Answer

Just move the condition on the left joined table from the where clause to the on clause of the join – otherwise they become mandatory, and rows where they are not fullfilled are filered out (here this removes rows that match but whose valy does not match {adifferentval}):

select a.val1,a.val2,b.valx
from a
left join b 
    on  b.akey = a.akey
    and b.valy = {adifferentval}
where a.akey = {somevalue}