Create table #tabla1 (clave varchar(2))
Create table #tabla2 (clave varchar(2), subclave int)
insert into #tabla1 values ('A')
insert into #tabla1 values ('B')
insert into #tabla1 values ('C')
insert into #tabla2 values ('B', 1)
insert into #tabla2 values ('B', 2)
insert into #tabla2 values ('B', 3)
insert into #tabla2 values ('B', 5)
Select
t1.clave,
subclave = case when t2.clave is null
then
0
else
t2.subclave
end
from #tabla1 t1
left join #tabla2 t2 on t1.clave = t2.clave
drop table #tabla1
drop table #tabla2