How many matches done after a left join?

[noshir_irani]

Hi,

I have a dataset a and I am left joining b on some keys a.x=b.x and a.y=b.y.

I want SAS to display how many matches happened. Right now it just gives the final number of rows in the final dataset. 

[Kurt_Bremser]

select
  a.*,
  case
    when a.x = b.x and a.y = b.y
    then 1
    else 0
  end as match

When no match is found, at least one of the b key variables will be missing.