Help to write an sql query

Question

Hi everyone!
I need some help in composing a query that would calculate the number of occurrences of '29-Feb' between 2 given dates (i.e. substitution variables).
What I figured so far is a way too complex and don't work all the time. Also I do know, that calculating a leap year is a bit different than just year mod 4 = 0.
I would appreciate very much if you help me to write this query or just give me a guess.
SELECT TO_NUMBER(TO_CHAR(date2, 'YYYY')-TO_CHAR(date1, 'YYYY'))/4
FROM
(SELECT CASE
WHEN MOD(TO_NUMBER(TO_CHAR(TO_DATE('&&date1', 'DD-Mon-RR'), 'RR')), 4) = 0
THEN TO_DATE('&date1', 'DD-Mon-RR')
ELSE(CASE
WHEN MOD(TO_NUMBER(TO_CHAR(ADD_MONTHS(TO_DATE('&date1', 'DD-Mon-RR'), 12), 'RR')), 4) = 0
THEN ADD_MONTHS(TO_DATE('&date1', 'DD-Mon-RR'), 12)
ELSE(CASE
WHEN MOD(TO_NUMBER(TO_CHAR(ADD_MONTHS(TO_DATE('&date1', 'DD-Mon-RR'), 24), 'RR')), 4) = 0
THEN ADD_MONTHS(TO_DATE('&date1', 'DD-Mon-RR'), 24)
ELSE(CASE
WHEN MOD(TO_NUMBER(TO_CHAR(ADD_MONTHS(TO_DATE('&date1', 'DD-Mon-RR'), 12), 'RR')), 4) = 0
THEN ADD_MONTHS(TO_DATE('&date1', 'DD-Mon-RR'), 36)
END)
END)
END)
END date1,
CASE
WHEN MOD(TO_NUMBER(TO_CHAR(TO_DATE('&&date2', 'DD-Mon-RR'), 'RR')), 4) = 0
THEN TO_DATE('&date2', 'DD-Mon-RR')
ELSE(CASE
WHEN MOD(TO_NUMBER(TO_CHAR(ADD_MONTHS(TO_DATE('&date2', 'DD-Mon-RR'), 12), 'RR')), 4) = 0
THEN ADD_MONTHS(TO_DATE('&date2', 'DD-Mon-RR'), 12)
ELSE(CASE
WHEN MOD(TO_NUMBER(TO_CHAR(ADD_MONTHS(TO_DATE('&date2', 'DD-Mon-RR'), 24), 'RR')), 4) = 0
THEN ADD_MONTHS(TO_DATE('&date2', 'DD-Mon-RR'), 24)
ELSE(CASE
WHEN MOD(TO_NUMBER(TO_CHAR(ADD_MONTHS(TO_DATE('&date2', 'DD-Mon-RR'), 12), 'RR')), 4) = 0
THEN ADD_MONTHS(TO_DATE('&date2', 'DD-Mon-RR'), 36)
END)
END)
END)
END date2
FROM DUAL);
UNDEFINE date1;
UNDEFINE date2;

Answer 1

Hi,
Interesting problem!
The query below looks at the 59th day after January 1 in each year.
If that date was in February, then it was a leap year.
If that date was not in February, then it was a common year.
DEFINE     date1     = "TO_DATE ('07-11-1609', 'DD-MM-YYYY')"
DEFINE     date2     = "TO_DATE ('06-11-2009', 'DD-MM-YYYY')"
WITH     all_years AS
     SELECT     ADD_MONTHS ( TRUNC (&date1, 'YYYY')
                  , 12 * (LEVEL - 1)
                  ) + 59       AS dt
     FROM     dual
     CONNECT BY     LEVEL <= 1 + CEIL ( MONTHS_BETWEEN ( &date2
                                                     , &date1
                           / 12
SELECT     COUNT ( CASE
               WHEN  TO_CHAR (dt, 'MM') = '02'
               THEN  1
          END
           )          AS leap_year_cnt
FROM     all_years
WHERE     dt     BETWEEN      &date1
          AND      &date2
;A less efficient (for what that's worth) way is to generate all dates between &date1 and &date2, and test each one to see if it is '02-29'.
I'll leave that as an exercise to the reader.
HINT: the coding is simpler than the query above. (In my prolix style, it took 10 lines. No sub-query is needed.)