SQL Server - INNER JOIN WITH DISTINCT

Try this:

select distinct a.FirstName, a.LastName, v.District
from AddTbl a 
  inner join ValTbl v
  on a.LastName = v.LastName
order by a.FirstName;

Or this (it does the same, but the syntax is different):

select distinct a.FirstName, a.LastName, v.District
from AddTbl a, ValTbl v
where a.LastName = v.LastName
order by a.FirstName;

I think you actually provided a good start for the correct answer right in your question (you just need the correct syntax). I had this exact same problem, and putting DISTINCT in a sub-query was indeed less costly than what other answers here have proposed.

select a.FirstName, a.LastName, v.District
from AddTbl a 
inner join (select distinct LastName, District 
    from ValTbl) v
   on a.LastName = v.LastName
order by Firstname   

add "distinct" after "select".

select distinct a.FirstName, a.LastName, v.District , v.LastName
from AddTbl a 
inner join ValTbl v  where a.LastName = v.LastName  order by Firstname