SQL & PL/SQL :: Use Greater And Less Than In Left Join?

I am creating a query where I am trying to take phone call lengths and put them into buckets of length ranges 0:00 - 0:59, 1:00 - 1:59 etc. Even if there are no calls in the call table I need to return the range with a zero (hence the left join and nvl). When I do this the left join acts like an equal join, I suspect there is some reason left joins only work if there is an equal condition in the join (instead of >= and < that I use, or similarly I could use BETWEEN). I also have a question about performance (below).

The create table script for the lookup is like this:

CREATE TABLE DURATION_RANGES
(
RANGE_TEXT varchar2(20),
RANGE_LBOUND decimal(22),
RANGE_UBOUND decimal(22)
)

Sample inserts are:

INSERT INTO DURATION_RANGES (RANGE_TEXT,RANGE_LBOUND,RANGE_UBOUND) VALUES ('00:00 - 00:59',0,59);
INSERT INTO DURATION_RANGES (RANGE_TEXT,RANGE_LBOUND,RANGE_UBOUND) VALUES ('01:00 - 01:59',60,119);
etc.

The query is:
select
r.range_text as duration_range,
nvl(count(*),0) as calls,
nvl(SUM(call_duration),0) as total_duration
from

[code]...

As I say, it is not returning all ranges in the duration_ranges table, so acting like an inner join. I realize one solution would be to populate duration ranges with every value possible (instead of ranges) so join is an equal join, but that would make the duration_range table larger.

My questions:
1. Is it possible to get the left join to work with the duration range values as they currently are?
2. Even if 1 is possible, would it be better performance to have exact values (but a larger lookup table) and do an equals join instead of >=, < or BETWEEN? Performance now is not bad.

What I mean is (with only one time value and not lbound and ubound:

INSERT INTO DURATION_RANGES (RANGE_TEXT,RANGE_LBOUND,RANGE_UBOUND) VALUES ('00:00 - 00:59',0);
INSERT INTO DURATION_RANGES (RANGE_TEXT,RANGE_LBOUND,RANGE_UBOUND) VALUES ('00:00 - 00:59',1);
INSERT INTO DURATION_RANGES (RANGE_TEXT,RANGE_LBOUND,RANGE_UBOUND) VALUES ('00:00 - 00:59',2);