Max(to_char(date,'DD-MM-YYYY')) ?

Question

Hi All,
SQL> desc hday;
Name Null? Type
H_DATE NOT NULL DATE
SQL> select max(h_date) from hday;
MAX(H_DATE
03-JAN-11
SQL> select max(to_char(h_date,'DD-MM-YY')) from hday;
MAX(TO_C
31-12-99
SQL> select max(to_char(h_date,'DD-MON-YY')) from hday;
MAX(TO_CH
31-MAY-99
My question is why am i getting different dates when i use different date formats in MAX function ?
any ideas ?
greddy

Answer 1

Always compare dates in date format. don't use to_char and then a function on top of it. Use the function on the date type. Also, check this out:
SQL> create table hday(h_date date);
Table created.
SQL> insert into hday values('03-JAN-11');
1 row created.
SQL> insert into hday values('31-MAY-99');
1 row created.
SQL> insert into hday values('31-DEC-99');
1 row created.
SQL> SELECT * FROM HDAY;
H_DATE
03-JAN-11
31-MAY-99
31-DEC-99
SQL>  SELECT TO_CHAR(H_DATE, 'DD-MON-YYYY')
  2   FROM HDAY;
TO_CHAR(H_D
03-JAN-2011
31-MAY-1999
31-DEC-1999
SQL> SELECT TO_CHAR(H_DATE, 'DD-MON-RRRR')
  2  FROM HDAY;
TO_CHAR(H_D
03-JAN-2011
31-MAY-1999
31-DEC-1999
SQL> select max(h_date)
  2  from hday;
MAX(H_DAT
03-JAN-11Now this makes a little more sense! In sumary, after y2k oracle recognizes any year before 1950 to be of the 2000's and any year after 1950 to be of the 1900's. For example, 00 is 2000 and not 1900. Also, 51 is 1951 and not 2051. To give you the exact terminology and logic behind I would have to look in the documentation. To avoid this problem, user four digit year when working with dates.
SQL> insert into hday values('03-JAN-1911');
1 row created.
SQL> SELECT TO_CHAR(H_DATE, 'DD-MON-YYYY')
  2  FROM HDAY;
TO_CHAR(H_D
03-JAN-2011
31-MAY-1999
31-DEC-1999
03-JAN-1911
SQL> select to_char(min(h_date), 'dd-mon-yyyy') dt
  2  from hday
  3  union
  4  select to_char(max(h_date), 'dd-mon-yyyy') dt
  5  from hday;
DT
03-jan-1911
03-jan-2011