how to handle date format using to_date function in oracle?

Question

I have a select query that consist an expression of TO_DATE(expiry_date, 'YYMM').

It works if expiry_date is in YYMM format. I want to set data as 0001 if expiry_date is in incorrect formats that are like YYM, YY,MM,YMM etc.

Is this possible?

Answer 1

Well, this is ugly, but seems to do the trick:

WITH data AS (
  SELECT '123' AS val FROM dual
  UNION SELECT '12' FROM dual
  UNION SELECT '1' FROM dual
  UNION SELECT '12345' FROM dual
  UNION SELECT '9612' FROM dual -- ok
  UNION SELECT '9613' FROM dual -- wrong
  UNION SELECT '1296' FROM dual -- wrong
  UNION SELECT 'AAAA' FROM dual -- wrong
)
SELECT
  CASE
    WHEN length(val) != 4
      OR NOT regexp_like(val, '[0-9]{4}')
      OR NOT to_number(substr(val, 3, 2)) BETWEEN 1 AND 12
    THEN to_date('0010', 'YYMM')
    ELSE to_date(val, 'YYMM')
  END AS date_yymm
FROM data;

Output:

DATE_YYMM
----------
01-10-2000
01-10-2000
01-10-2000
01-10-2000
01-10-2000
01-12-2096
01-10-2000
01-10-2000

Or you can just use a function:

CREATE OR REPLACE FUNCTION is_date_format(p_value IN VARCHAR2, p_format IN VARCHAR2) RETURN NUMBER
AS
  l_dummy DATE;
BEGIN
  l_dummy := to_date(p_value, p_format);
  RETURN 0;
EXCEPTION
  WHEN OTHERS THEN
    RETURN 1;
END;
/

WITH data AS (
  SELECT '123' AS val FROM dual
  UNION SELECT '12' FROM dual
  UNION SELECT '1' FROM dual
  UNION SELECT '12345' FROM dual
  UNION SELECT '9612' FROM dual -- ok
  UNION SELECT '9613' FROM dual -- wrong
  UNION SELECT '1296' FROM dual -- wrong
)
SELECT
  -- fx for exact matching as pointed out by Nicholas Krasnov
  DECODE(is_date_format(val, 'fxYYMM'), 0, val, '0010')
FROM data;

Answer 2

SELECT  CASE
            WHEN LENGTH(expiry_date) = 4
            THEN TO_DATE(expiry_date, 'YYMM')
            ELSE TO_DATE('0001', 'YYMM')
        END AS d_date
FROM
(
        SELECT 1212 expiry_date FROM DUAL UNION ALL
        SELECT 1211             FROM DUAL UNION ALL
        SELECT 1210             FROM DUAL UNION ALL
        SELECT 121              FROM DUAL UNION ALL
        SELECT 12               FROM DUAL
)
;
/*
2012-12-01 00:00:00
2012-11-01 00:00:00
2012-10-01 00:00:00
2000-01-01 00:00:00
2000-01-01 00:00:00
*/

Something like this?