Search varchar2 for a format? - sql

Question

How do you query varchar2 for a format? Example is Varchar2 field containing date as mm/dd/yyyy '01/01/2015'. How would I find a date that was written as yyyy/mm/dd '2015/01/01' as I do not know the incorrectly formatted date so i can't literally search it. I just want to write where FIELD_1 like '####/##/##' but that obviously does not work.

Answer 1

Of course what you want to do works, if you use regular expressions:
where regexp_like(field_1, '^[0-9]{4}/[0-9]{2}/[0-9]{2}$')
As a side note: you should not be storing dates in the database as strings. You should be using dates instead.

Answer 2

Gordon's answer is probably good enough for what you need, but it may be an issue that the regular expression he gave you will match things like 9999/99/99 that are not dates.
If you really need to match dates -- and if the date is the entire value of the VARCHAR2 and not just embedded somewhere in it -- then a function can help.
In the below example, I create a function called safe_to_date that returns a NULL if the given VARCHAR2 value is not a date in the specified format.
CREATE OR REPLACE FUNCTION safe_to_date ( p_string VARCHAR2 ) RETURN DATE IS
BEGIN
RETURN to_date(p_string,'YYYY/MM/DD');
EXCEPTION
WHEN others THEN
RETURN NULL;
END;
with my_table AS
( SELECT '9999/99/99' /*invalid*/ my_column FROM dual UNION ALL
SELECT '2015/12/25' from dual UNION ALL
SELECT 'not a date at all' /*invalid*/ FROM dual UNION ALL
SELECT '11-NOV-1917' from dual UNION ALL
SELECT '2015*DEC*25' from dual UNION ALL
SELECT '2015/02/28' from dual UNION ALL
SELECT '2015/02/29' /*invalid*/ from dual)
SELECT *
FROM my_table
WHERE safe_to_date(my_column) IS NOT NULL;
Expected results:
25-DEC-2015
11-NOV-1917
25-DEC-2015
28-FEB-2015