Oracle - Cycle detected while executing recursive 'WITH' query - database

Question

I'm doing a basic example of recursive query with oracle sql. I'm computing future months of the format MON-YY. I managed to have a seemingly correct query but I don't understand the break condition with a WITH query.
I'm trying to break on the year value (for example stop when you reach 2020), but it detects a cycle while doing that. If I break on the month value (e.g. December), it works.
Here's my query with a month based break:
with
prochains_mois(mois, annee) as (
select 'sep' as mois, 19 as annee
from dual
union all
select
case mois
when 'jan' then 'fev'
when 'fev' then 'mar'
when 'mar' then 'avr'
when 'avr' then 'mai'
when 'mai' then 'jun'
when 'jun' then 'jui'
when 'jui' then 'aou'
when 'aou' then 'sep'
when 'sep' then 'oct'
when 'oct' then 'nov'
when 'nov' then 'dec'
when 'dec' then 'jan'
end,
case mois
when 'dec' then annee + 1
else annee
end
from prochains_mois r
where mois <> 'dec'
)
select * from prochains_mois;
If I do this, it returns a consistent result.
MOI ANNEE
--- ----------
sep 19
oct 19
nov 19
dec 19
Now if I try to break the recursive query on the year, let's say 2020, so I change the where condition in the with clause to :
where annee < 20
Then I get :
ORA-32044: cycle detected while executing recursive WITH query
I tried to break with a later month to see if my year addition works correctly, it seems to be the case. If I break on march, I get the January and February correctly :
where mois <> 'mar'
gives
MOI ANNEE
--- ----------
sep 19
oct 19
nov 19
dec 19
jan 20
fev 20
mar 20

Answer 1

Use DATEs:
with prochains_mois( value ) as (
select DATE '2019-09-01' from dual
union all
select ADD_MONTHS( value, 1 )
FROM prochains_mois
WHERE value < DATE '2020-12-01'
)
select SUBSTR( TO_CHAR( value, 'mon', 'NLS_DATE_LANGUAGE=FRENCH' ), 1, 3 ) AS mois,
TO_CHAR( value, 'RR' ) AS annee
from prochains_mois;
Output:
MOIS | ANNEE
:--- | :----
sep | 19
oct | 19
nov | 19
dec | 19
jan | 20
fev | 20
mar | 20
avr | 20
mai | 20
jui | 20
jui | 20
aou | 20
sep | 20
oct | 20
nov | 20
dec | 20
or use your query and check that the month and year do not match:
with
prochains_mois(mois, annee) as (
select 'sep' as mois, 19 as annee
from dual
union all
select
case mois
when 'jan' then 'fev'
when 'fev' then 'mar'
when 'mar' then 'avr'
when 'avr' then 'mai'
when 'mai' then 'jun'
when 'jun' then 'jui'
when 'jui' then 'aou'
when 'aou' then 'sep'
when 'sep' then 'oct'
when 'oct' then 'nov'
when 'nov' then 'dec'
when 'dec' then 'jan'
end,
case mois
when 'dec' then annee + 1
else annee
end
from prochains_mois r
where ( mois, annee ) NOT IN ( ( 'dec', 20 ) )
)
select * from prochains_mois;
Output:
MOIS | ANNEE
:--- | ----:
sep | 19
oct | 19
nov | 19
dec | 19
jan | 20
fev | 20
mar | 20
avr | 20
mai | 20
jun | 20
jui | 20
aou | 20
sep | 20
oct | 20
nov | 20
dec | 20
db<>fiddle here

Answer 2

Your main issue is that you're trying to manipulate dates using strings/numbers. Don't do that; if you're working with dates, use dates!
E.g. you can do what you're after like so:
WITH prochains_mois (mnth_dt) AS (SELECT TRUNC(sysdate, 'mm') mnth_dt
FROM dual
UNION ALL
SELECT add_months(mnth_dt, 1) mnth_dt
FROM prochains_mois
WHERE add_months(mnth_dt, 1) < add_months(TRUNC(sysdate, 'yyyy'), 12))
SELECT mnth_dt,
to_char(mnth_dt, 'mon') mois,
to_char(mnth_dt, 'yy') annee
FROM prochains_mois;
MNTH_DT MOIS ANNEE
----------- ---- -----
01/09/2019 sep 19
01/10/2019 oct 19
01/11/2019 nov 19
01/12/2019 dec 19
N.B. You could simplify the predicate in the recursive sub-factored query to mnth_dt < add_months(TRUNC(SYSDATE, 'yyyy'), 11).
This works by taking the start date (here, I've used sysdate) and finding the first of the month (by using the optional second parameter of TRUNC to specify the level we're truncating it to).
Then we simply add a month to each date until we hit the last month of the start date's year.
Only after you've got the dates do you then output the data in the format you require using to_char.