The SELECT clause specifies the columns for the table MATCH. SQL expressions in the SELECT clause calculate the differences for the appropriate columns and create new columns. 
proc sql;
   create table match as
      select
         one.Low,
         one.Pair,
         (one.lwt - two.lwt) as Lwt_d,
         (one.smoke - two.smoke) as Smoke_d,
         (one.ptd - two.ptd) as Ptd_d,
         (one.ht - two.ht) as Ht_d,
         (one.ui - two.ui) as UI_d