Postgresql : Query were each join result is a line

I got a database structure with three tables. On table containing some ids and two table containing the same row and a foreign key on the first table :

Table A:
id
1
2
3

Table B:
a_id    row_abc 
1       value1
2       value3
3       value6

Table C:
a_id    row_abc
1       value2
2       value7
4       value9

How to get a result looking like this (a kind of left join were each result is displayed in lines instead of in additional columns in the result):

id      row_abc
1       value1
1       value2
2       value3
2       value7
3       value6
4       value9

Answer

I think you want union all:

select a_id as id, row_abc
from b
union all
select a_id, row_abc
from c;