--disable_warnings
drop table if exists t1,t2;
--enable_warnings
create table t1 (a int primary key auto_increment, b int);
create table t2 (c int primary key auto_increment, d int);

let $count= 100;
while ($count)
{
  INSERT INTO t1 VALUES ();
  INSERT INTO t2 VALUES ();
  dec $count;
}

EXPLAIN SELECT * FROM t1 FORCE INDEX (PRIMARY) JOIN t2 ON b=c ORDER BY a LIMIT 2;
EXPLAIN SELECT * FROM t1 FORCE INDEX (PRIMARY) JOIN t2 ON a=c ORDER BY a LIMIT 2;