how to use nvl on a regexp_like product - oracle

Question

please can someone help with a SQL problem?
I have a query which currently accepts an external parameter which can be null or a single value such as 'STR1' .
This is handled by a query in format below:
select a.refe_id from a, b, c
where a.owln_code = c.code
and c.con_id = b.pers_id
and b.con_abbrv = nvl(:PARAM, b.con_abbrv)
and a.status = '01'
In the future the external parameter can have a single value, null, or multiple values separated by pipes e.g STR1|STR2|STR3|
I am now at the stage below in accomodating this but have lost the nvl test that allows a match through all rows in table b if the parameter is null.
Please can someone help with how to do this? I have searched the net and tried to do it myself. Thanks very much in advance.
select a.refe_id from a, b, c
where a.owln_code = c.code
and c.con_id = b.pers_id
and regexp_like(:PARAM, '(^|)' || b.con_abbrv|| '(|$)')
and a.status = '01'

Answer 1

I'd recommend something like this:
select a.refe_id from a, b, c
where a.owln_code = c.code
and c.con_id = b.pers_id
and (:PARAM IS NULL OR regexp_like(:PARAM, '(^|)' || b.con_abbrv|| '(|$)'))
and a.status = '01'
Not related, but I'd also recommend using explicit join syntax: I think you'll find it makes the query easier to read because it separates the JOIN logic from the WHERE logic:
select a.refe_id from a
join c on a.owln_code = c.code
join b on c.con_id = b.pers_id
where (:PARAM IS NULL OR regexp_like(:PARAM, '(^|)' || b.con_abbrv|| '(|$)'))
and a.status = '01'