REGEXP_SUBSTR not able to process only current row - oracle

Question

(SELECT LISTAGG(EVENT_DESC, ',') WITHIN GROUP (ORDER BY EVENT_DESC) FROM EVENT_REF WHERE EVENT_ID IN
( SELECT REGEXP_SUBSTR(AFTER_VALUE,'[^,]+', 1, level) FROM DUAL
CONNECT BY REGEXP_SUBSTR(AFTER_VALUE, '[^,]+', 1, level) IS NOT NULL
)
)
A table from which I am fetching AFTER_VALUE has values of integer which is comma seperated like
AFTER_VALUE data
Expected output
1
Event1
1,2
Event1,Event2
1,12,2,5
Event1,Event12,Event2,Event5
15,13
Event15,Event13
these are Ids in EVENT_REF table which have some description. I am trying to basically present
ex. 1,2 as Event1, Event2 and send back from query. There are multiple events so using REPLACE would be very tedious.
When using above query I'm getting error as “ORA-01722: invalid number” whenever there is more than one value in AFTER_VALUE column Ex. if there exists only one id , then the query works but for values like 1,2 or 1,13 etc it throws invalid number error.
PS: The event names are not Event1,Event2 etc , I have just put for reference.

Answer 1

You don't even need regular expressions for this assignment. Standard string function replace() can do the same thing, and faster. You only need an extra 'Event' at the beginning of the string, since that one doesn't "replace" anything.
Like this: (note that you don't need the with clause; I included it only for quick testing)
with
event_ref (after_value) as (
select '1' from dual union all
select '1,2' from dual union all
select '1,12,2,5' from dual union all
select '15,13' from dual
)
select after_value,
'Event' || replace(after_value, ',', ',Event') as desired_output
from event_ref
;
AFTER_VALUE DESIRED_OUTPUT
----------- -----------------------------
1 Event1
1,2 Event1,Event2
1,12,2,5 Event1,Event12,Event2,Event5
15,13 Event15,Event13

Answer 2

Ah,ok, looks, like you have other characters in your comma-separated list, so you can use this query:
with EVENT_REF(EVENT_ID,EVENT_DESC) as (
select 1, 'Desc 1' from dual union all
select 2, 'Desc 2' from dual union all
select 3, 'Desc 3' from dual union all
select 4, 'Desc 4' from dual union all
select 5, 'Desc 5' from dual union all
select 12, 'Desc12' from dual union all
select 13, 'Desc13' from dual union all
select 15, 'Desc15' from dual
)
select
(SELECT LISTAGG(EVENT_DESC, ',')
WITHIN GROUP (ORDER BY EVENT_DESC)
FROM EVENT_REF
WHERE EVENT_ID IN
( SELECT to_number(REGEXP_SUBSTR(AFTER_VALUE,'\d+', 1, level))
FROM DUAL
CONNECT BY level<=REGEXP_COUNT(AFTER_VALUE, '\d+')
)
)
from (
select '1' AFTER_VALUE from dual union all
select '1,2' AFTER_VALUE from dual union all
select '1,12,2,5' AFTER_VALUE from dual union all
select '15,13' AFTER_VALUE from dual
);
PS. And do not forget that to_number has 'default on conversion error' now: https://docs.oracle.com/en/database/oracle/oracle-database/12.2/sqlrf/TO_NUMBER.html

Answer 3

There is no need to split and concatenate substrings, just use regexp_replace:
with EVENT_REF (AFTER_VALUE) as (
select '1' from dual union all
select '1,2' from dual union all
select '1,12,2,5' from dual union all
select '15,13' from dual
)
select regexp_replace(AFTER_VALUE,'(\d+)','Event\1') from EVENT_REF;
REGEXP_REPLACE(AFTER_VALUE,'(\D+)','EVENT\1')
-----------------------------------------------
Event1
Event1,Event2
Event1,Event12,Event2,Event5
Event15,Event13