Working with dates in PL SQL - sql

Question

I have a simple PL SQL code. However it is failing at date level. The date column is CODT. I declared CODT as date. And in database level, it is date with format YYYY-MM-DD.
I also tried alter session set nls_date_format = 'YYYY-MM-DD'; But it is throwing error.
The error message is ORA-01830: date format picture ends before converting entire input string
00000 - "date format picture ends before converting entire input string"
Could you let me know where I need to change it to date format/ where I am making a mistake ?
DECLARE
RID VARCHAR2(100);
KY VARCHAR2(200);
CODT DATE;
CURSOR FETCH_DTLS IS
SELECT ROW_ID,
KEY,
CUT_OFF_DT,
FROM TMP1
WHERE RN = 1;
BEGIN
OPEN FETCH_DTLS;
LOOP
FETCH FETCH_DTLS
INTO RID,
KY,
CODT;
EXIT WHEN FETCH_DTLS%NOTFOUND;
INSERT INTO tmp2
VALUES
(RID,
KY,
CODT
);
END LOOP;
COMMIT;
CLOSE FETCH_DTLS;
COMMIT;
END;

Answer 1

if you have date column which defined varchar2 in db you should use it like this:to_date(your_column/*CUT_OFF_DT*/, 'yyyy-mm-dd')

Answer 2

when you use VARCHAR2 field and insert it in a table with DATE data-type, then you tell oracle to: Cast VARCHAR2 to DATE
So your mistake is casting without providing any format, here are some date format examples used in oracle:
'YYYY-MM-DD'
'YYYY-MM-DD HH24:MI:SS'
there is also another function in oracle called TO_DATE which will do the job, it simply casts the string(char or varchar) to date with provided date-format and also provided calendar! Here is some examples:
TO_DATE('2016-12-15','YYYY-MM-DD')--uses default calendar of session
TO_DATE('2016-12-15','YYYY-MM-DD', 'nls_calendar=gregorian')
TO_DATE('1395-09-25','YYYY-MM-DD', 'nls_calendar=persian')--Solar base date used in IRAN
and reverse function is TO_CHAR
TO_CHAR(SYSDATE,'YYYY-MM-DD')--SYSDATE is in Date type so this works
there is another data-type related to dates, which is called TIMESTAMP
TO_CHAR(SYSTIMESTAMP,'YYYY-MM-DD HH24:MI:SSxFF')--SYSTIMESTAMP is in TIMESTAMP type so this works
finally we can use INTERVAL type to calculate interval between 2 dates(Specially timestamps) and there is a useful function called numtodsinterval which converts numbers to intervals, you can use it like this:
SYSDATE+NUMTODSINTERVAL(1,'Minute')
and this is an example:
SELECT TO_CHAR(SYSDATE,'YYYY-MM-DD HH24:MI:SS'),
TO_CHAR(SYSDATE+NUMTODSINTERVAL(1,'Minute'),'YYYY-MM-DD HH24:MI:SS')
FROM DUAL
which outputs:
1 2016-12-15 15:05:10 2016-12-15 15:06:10
I hope it will be useful in your future usages of DATE, goodluck