Trying to create a sequence, from 3 fields

Question

I need to come up with a mechanism to generate the primary key for a table.
the table looks something like
Co | Permit | Episode | a | b | c | Co2 | Permit2
the co2 and permit2 are foreign keys to another table. Co and Permit are just copies of Co2 and Permit2. So then I am adding another field "Episode" to create the primary key.
so I would have something like
1-00001-1 a b c 1-00001
1-00001-2 a b c 1-00001
1-00002-1 a b c 1-00002
1-00002-2 a b c 1-00002
1-00002-3 a b c 1-00002
1-00003-1 a b c 1-00003
I wanted to use a seq to generate this, but since it is multiple fields it is not a continues number where a 1 or multiple needs added on. Do I use a sequence here? Trigger?
Any suggestions?

Answer 1

John,
I am not necessarily saying that this is the way to go, but am just providing you with what you originally asked for, as an option to consider. The following trigger would insert numbers into the episode column in the manner that you specified:
CREATE OR REPLACE TRIGGER episode_trigger
BEFORE INSERT ON table_name
FOR EACH ROW
BEGIN
SELECT MAX (temp_max)
INTO :NEW.episode
FROM (SELECT 1 temp_max
FROM DUAL
UNION
SELECT MAX (episode) + 1 temp_max
FROM table_name
WHERE co = :NEW.co
AND permit = :NEW.permit);
END episode_trigger;
null