create table t1 (
   val1 varchar(10) primary key,
   val2 varchar(10)
)

create table t2 (
   tmp1 varchar(10) primary key,
   tmp2 varchar(10)
)

##</code><code>##

select t1.val2, t2.tmp2
from t1 join t2 on val2=tmp2

##</code><code>##

select t1.val2, t2.tmp2
from t1 join t2 on val1=tmp1