drop table if exists sub_tab;
drop table if exists main_tab;
drop table if exists flag_1;
drop table if exists flag_2;
create temporary table flag_1 ( flag_1_id integer primary key, flag_1_t
text );
insert into flag_1 values (0, null ), ( 1, 'a' ), ( 2, 'b' ), ( 3, 'c' );
create temporary table flag_2 ( flag_2_id integer primary key, flag_2_t
text );
insert into flag_2 values (0, null ), ( 1, 'a' ), ( 2, 'b' ), ( 3, 'c' );
create temporary table main_tab ( main_id integer primary key, main_t
text, flag_1_id integer references flag_1 ( flag_1_id ) );
insert into main_tab values ( 1, 'Main 1', 1 ), ( 2, 'Main 2', 2 ), ( 3,
'Main 3', 3 );
create temporary table sub_tab ( sub_id integer primary key, sub_t
text, main_id integer references main_tab ( main_id ), flag_1_id integer
references flag_1 ( flag_1_id ), flag_2_id integer references flag_2 (
flag_2_id ) );
insert into sub_tab values ( 1, 'Sub 1', 1, 3, 1 ), ( 2, 'Sub 2', 2, 2,
2 ), ( 3, 'Sub 3', 3, 1, 3 );
select m.main_id, m.main_t, f.flag_1_t,
x.sub_id, x.sub_t, x.flag_1_t, x.flag_2_t
from main_tab as m
join flag_1 as f using ( flag_1_id )
left join
(
sub_tab as s
join flag_2 as f2 using ( flag_2_id ) -- that
way it works
join flag_1 as f using ( flag_1_id )
-- join flag_2 as f2 using ( flag_2_id ) -- that
way it doesn't work
) as x using ( main_id );
