How to find a specific mask within a string - Oracle? - string

Question

I have a field in a table that can be informed with differente values.
Examples:
Row 1 - (2012,2013)
Row 2 - 8871
Row 3 - 01/04/2012
Row 4 - 'NULL'
I have to identify the rows that have a string with a date mask 'dd/mm/yyyy' informed. Like Row 3, so I may add a TO_DATE function to it.
Any idea on how can I search a mask within the field?
Thanks a lot

Answer 1

Sounds like a data model problem (storing a date in a string).
But, since it happens and we sometimes can't control or change things, I usually keep a function around like this one:
CREATE OR REPLACE FUNCTION safe_to_date (p_string IN VARCHAR2,
p_format_mask IN VARCHAR2,
p_error_date IN DATE DEFAULT NULL)
RETURN DATE
DETERMINISTIC IS
x_date DATE;
BEGIN
BEGIN
x_date := TO_DATE (p_string, p_format_mask);
RETURN x_date; -- Only gets here if conversion was successful
EXCEPTION
WHEN OTHERS THEN
RETURN p_error_date;
END;
END safe_to_date;
Then use it like this:
WITH d AS
(SELECT 'X' string_field FROM DUAL
UNION ALL
SELECT '11/15/2012' FROM DUAL
UNION ALL
SELECT '155' FROM DUAL)
SELECT safe_to_date (d.string_field, 'MM/DD/YYYY')
FROM d;

Answer 2

SQL Fiddle
Oracle 11g R2 Schema Setup:
CREATE TABLE Test ( id, VALUE ) AS
SELECT 'Row 1', '(2012,2013)' FROM DUAL
UNION ALL SELECT 'Row 2', '8871' FROM DUAL
UNION ALL SELECT 'Row 3', '01/04/2012' FROM DUAL
UNION ALL SELECT 'Row 4', NULL FROM DUAL
UNION ALL SELECT 'Row 5', '99,99,2015' FROM DUAL
UNION ALL SELECT 'Row 6', '32/12/2015' FROM DUAL
UNION ALL SELECT 'Row 7', '29/02/2015' FROM DUAL
UNION ALL SELECT 'Row 8', '29/02/2016' FROM DUAL
/
Query 1 - You can check with a regular expression:
SELECT *
FROM TEST
WHERE REGEXP_LIKE( VALUE, '^\d{2}/\d{2}/\d{4}$' )
Results:
| ID | VALUE |
|-------|------------|
| Row 3 | 01/04/2012 |
| Row 6 | 32/12/2015 |
| Row 7 | 29/02/2015 |
| Row 8 | 29/02/2016 |
Query 2 - You can make the regular expression more complicated to catch more invalid dates:
SELECT *
FROM TEST
WHERE REGEXP_LIKE( VALUE, '^(0[1-9]|[12]\d|3[01])/(0[1-9]|1[0-2])/\d{4}$' )
Results:
| ID | VALUE |
|-------|------------|
| Row 3 | 01/04/2012 |
| Row 7 | 29/02/2015 |
| Row 8 | 29/02/2016 |
Query 3 - But the best way is to try and convert the value to a date and see if there is an exception:
CREATE OR REPLACE FUNCTION is_Valid_Date(
datestr VARCHAR2,
format VARCHAR2 DEFAULT 'DD/MM/YYYY'
) RETURN NUMBER DETERMINISTIC
AS
x DATE;
BEGIN
IF datestr IS NULL THEN
RETURN 0;
END IF;
x := TO_DATE( datestr, format );
RETURN 1;
EXCEPTION
WHEN OTHERS THEN
RETURN 0;
END;
/
SELECT *
FROM TEST
WHERE is_Valid_Date( VALUE ) = 1
Results:
| ID | VALUE |
|-------|------------|
| Row 3 | 01/04/2012 |
| Row 8 | 29/02/2016 |

Answer 3

You can use the like operator to match the pattern.
where possible_date_field like '__/__/____';