oracle between month name - sql

Question

My output without where clause ( sample )
ID
NAMEN
NAME
BEGINN
ENDE
108129
Kürbis, Gartenkürbis, Feldkürbis
Blüten
Juli
Juli
126611
Nussbaum, Walnuss, Christnuss
Schalen
August
September
126611
Nussbaum, Walnuss, Christnuss
Früchte
Oktober
Oktober
126611
Nussbaum, Walnuss, Christnuss
Blätter
Juni
Juni
92542
Beifuß Stabkraut, Besenkraut
Blätter
Juni
Juni
92542
Beifuß Stabkraut, Besenkraut
Wurzeln
September
November
Hi i try to select entries between beginn (e.g Juli) and ende (e.g. Dezember) (varchar2).
select * from (
select * from VIEW_USER_CON_PFLANZE_ERNTE
)
where sysdate
between to_date(beginn, 'MONTH', 'NLS_DATE_LANGUAGE=German')
and to_date(ende, 'MONTH', 'NLS_DATE_LANGUAGE=German')
but i get the error: ORA-01843: not a valid month
at the end, i want to realize this:
where sysdate
...
and last_day(to_date(ende, 'DD.MONTH', 'NLS_DATE_LANGUAGE=German'))
the select of to_date(beginn, 'MONTH', 'NLS_DATE_LANGUAGE=German')* and *to_date(ende, 'MONTH', 'NLS_DATE_LANGUAGE=German') from dual works and i get MM/DD/YYYY for both

Answer 1

Most likely there are invalid months names in your table. Another proof that you should never store date/time values as string. Use always proper DATE/TIMESTAMP data type.
If you use Oracle 18 or newer, then you can find invalid values like this:
SELECT *
FROM VIEW_USER_CON_PFLANZE_ERNTE
WHERE
TO_DATE(beginn DEFAULT NULL ON CONVERSION ERROR, 'MONTH', 'NLS_DATE_LANGUAGE=German') IS NULL
OR
TO_DATE(ende DEFAULT NULL ON CONVERSION ERROR, 'MONTH', 'NLS_DATE_LANGUAGE=German') IS NULL
or this one:
WITH t AS (
SELECT beginn, ende,
VALIDATE_CONVERSION(beginn AS DATE, 'MONTH', 'NLS_DATE_LANGUAGE=German') as begin_valid,
VALIDATE_CONVERSION(ende AS DATE, 'MONTH', 'NLS_DATE_LANGUAGE=German') as end_valid
FROM VIEW_USER_CON_PFLANZE_ERNTE)
SELECT *
FROM t
WHERE begin_valid= 0 or end_valid = 0

Answer 2

okay my solution is simple... I found some exceptions in my field values of the underlying table and removed them... it works...
learnings
just because the view works, the underlying table doesn't work, so you can't use a where between clause even if your view works
if it not work, search for exception in your fields
and don't use varchar2 for date comparison unless absolutely necessary

Answer 3

It is really a bad practice to store date fields as varchar2. I have seen it many times and it is always a source for problems and issues.
Looking are your data sample, it looks to me like the reason why you got the error is because you really have invalid months in your data. I am not even considering that the "between" you are applying lacks of basic logic, as between should include both respectively. The reason is the conversion from to_date from a month that gives you the first day at midnight. Perhaps you should consider using last_day as well in order to include the data of the second month used in the between condition.
Demonstration
SQL> create table t1 ( c1 varchar2(30) , c2 varchar2(30) ) ;
Table created.
SQL> insert into t1 values ( 'JANUAR' , 'MAI' ) ;
1 row created.
SQL> insert into t1 values ( 'JANUAR' , 'FEBRUAR' );
1 row created.
SQL> select * from t1 ;
C1 C2
------------------------------ ------------------------------
JANUAR MAI
JANUAR FEBRUAR
So, now we have two fields with varchar2 data type but they contain the month in German Language. Applying your filter works perfectly
SQL> select to_date(c1,'MONTH', 'NLS_DATE_LANGUAGE=German' ) as c1 ,
2 to_date(c2, 'MONTH', 'NLS_DATE_LANGUAGE=German' ) as c2,
3 sysdate-180 as date_calculation
4 from t1
5 where sysdate-180 between to_date(c1,'MONTH', 'NLS_DATE_LANGUAGE=German' )
6* and to_date(c2, 'MONTH', 'NLS_DATE_LANGUAGE=German' )
SQL> /
C1 C2 DATE_CALC
--------- --------- ---------
01-JAN-21 01-MAY-21 25-MAR-21
The only possible explanation is that you have indeed data which is not a valid month. You can use the answer provided by #Wernfried Domscheit to find out which rows don't contain valid months.
db<>fiddle