Oracle - Extract Year from date result in 0 [duplicate] - oracle

Question

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Trying to export a Oracle via PL/SQL gives a date of 0000-00-00
(1 answer)
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Duplicate of Trying to export a Oracle via PL/SQL gives a date of 0000-00-00 as mentioned by #AlexPoole
I have a table with different dates in it, however, when I try to extract year, a single row returns an incorrect result.
This incorrect result happens when I execute the following (note that TO_DATE and FROM_DATE are both of data_type DATE):
select
TO_DATE
,EXTRACT(YEAR FROM TO_DATE) as "TO_YEAR"
,EXTRACT(MONTH FROM TO_DATE) as "TO_MONTH"
,EXTRACT(DAY FROM TO_DATE) as "TO_DAY"
,FROM_DATE
,EXTRACT(YEAR FROM FROM_DATE) as "FROM_YEAR"
,EXTRACT(MONTH FROM FROM_DATE) as "FROM_MONTH"
,EXTRACT(DAY FROM FROM_DATE) as "FROM_DAY"
,DUMP(FROM_DATE, 1016) as FROM_DUMP
,to_char(FROM_DATE, 'SYYYY-MM-DD HH24:MI:SS') FROM_STRING
from SomeTable
The incorrect result is (date format is YY-MM-DD):
TO_DATE TO_YEAR TO_MONTH TO_DAY FROM_DAT FROM_YEAR FROM_MONTH FROM_DAY FROM_DUMP FROM_STRING
-------- ---------- ---------- ---------- -------- ---------- ---------- ---------- ----------------------------- --------------------
00-02-01 2000 2 1 01-02-01 0 2 1 Typ=12 Len=7: 64,64,2,1,1,1,1 00000-00-00 00:00:00
My question is why does FROM_YEAR return a zero and not 2001?

Answer 1

A DATE is stored in 7-bytes using:
century + 100
year-of-century + 100
month + 0
day + 0
hour + 1
minute + 1
second + 1
Looking at the output of DUMP, which is Typ=12 Len=7: 64,64,2,1,1,1,1 then you have:
Century = -36
Year-of-century = -36
Month = February
Day = 1
Hour = 0
Minute = 0
Year = 0
Which would make your date midnight of 1st February 3636 BC.
Unless you intended to use dates from ancient history then it would suggest that somewhere in your application some corrupted data has been stored.
However, something else appears to be going on as that is a valid date that can be stored and TO_CHAR should work.
CREATE TABLE table_name ( dt ) AS
SELECT DATE '-3636-02-01'FROM DUAL;
SELECT TO_CHAR( dt, 'SYYYY-MM-DD HH24:MI:SS' ) AS dt_string,
DUMP( dt )
FROM table_name;
Outputs:
DT_STRING
DUMP(DT)
-3636-02-01 00:00:00
Typ=12 Len=7: 64,64,2,1,1,1,1
db<>fiddle here
and the DUMP matches your data but the TO_CHAR output is valid whereas yours is zeros.