create table T1 (ID int, COL int);
create index T1_ID on T1 (ID);
create unique index T1_COL on T1 (COL);

create table T2 (ID int);
create index T2_ID on T2 (ID);

create table T3 (ID int);
create index T3_ID on T3 (ID);


select *
from T1
join T2 on T2.ID = T1.ID
join T3 on T3.ID = coalesce(T1.ID, T2.ID)
where T1.COL = ?

-- bad plan by FB 1.5
-- PLAN JOIN (T3 NATURAL, T1 INDEX (T1_COL), T2 INDEX (T2_ID))

-- bad plan by FB 2.x
-- PLAN MERGE (SORT (JOIN (T1 INDEX (T1_COL), T2 INDEX (T2_ID))), SORT (T3 NATURAL))

-- expected plan
-- PLAN JOIN (T1 INDEX (T1_COL), T2 INDEX (T2_ID), T3 INDEX (T3_ID))