How to normalize DATE using BEFORE INSERT Trigger / PLSQL Procedure [duplicate] - oracle

Question

ACTUAL
expected
SEP-10-2017
10-SEP-2017
SEP 30 2018
30-SEP-2018
OFFICE OF SMALL
OCT-11-2018
11-OCT-2018
O9-SEP-2009
O9-SEP-2009
Not Applicable
NOV-20-2001
20-NOV-2001
BANIJYA BHIBAG
AUGUST 03 2017
03-AUG-2017
AUG-04-1991
04-AUG-1991
97/2015
09/09/2018
09-SEP-2018
how can we get the result as above and discard the date that cannot be converted?

Answer 1

From Oracle 12, you do not need PL/SQL and can use:
SELECT actual,
COALESCE(
TO_DATE(
actual DEFAULT NULL ON CONVERSION ERROR,
'MM-DD-YYYY',
'NLS_DATE_LANGUAGE=ENGLISH'
),
TO_DATE(
actual DEFAULT NULL ON CONVERSION ERROR,
'DD-MON-YYYY',
'NLS_DATE_LANGUAGE=ENGLISH'
)
) AS parsed
FROM table_name;
Which, for the sample data:
CREATE TABLE table_name (ACTUAL) AS
SELECT 'SEP-10-2017' FROM DUAL UNION ALL
SELECT 'SEP 30 2018' FROM DUAL UNION ALL
SELECT 'OFFICE OF SMALL' FROM DUAL UNION ALL
SELECT 'OCT-11-2018' FROM DUAL UNION ALL
SELECT 'O9-SEP-2009' FROM DUAL UNION ALL
SELECT 'Not Applicable' FROM DUAL UNION ALL
SELECT 'NOV-20-2001' FROM DUAL UNION ALL
SELECT 'BANIJYA BHIBAG' FROM DUAL UNION ALL
SELECT 'AUGUST 03 2017' FROM DUAL UNION ALL
SELECT 'AUG-04-1991' FROM DUAL UNION ALL
SELECT '97/2015' FROM DUAL UNION ALL
SELECT '09/09/2018' FROM DUAL;
Outputs:
ACTUAL
PARSED
SEP-10-2017
10-SEP-2017
SEP 30 2018
30-SEP-2018
OFFICE OF SMALL
OCT-11-2018
11-OCT-2018
O9-SEP-2009
Not Applicable
NOV-20-2001
20-NOV-2001
BANIJYA BHIBAG
AUGUST 03 2017
03-AUG-2017
AUG-04-1991
04-AUG-1991
97/2015
09/09/2018
09-SEP-2018
Note: O9-SEP-2009 has not parsed because you have the letter O rather than the digit 0 as the first character.
db<>fiddle here

Answer 2

One option is to create a function which will cover all possible combinations. The following example has some of them - you'd have to add new when you find them.
SQL> create or replace function f_date (par_str in varchar2)
2 return date
3 is
4 l_date date;
5 begin
6 begin
7 l_date := to_date(par_str, 'mon-dd-yyyy');
8 return l_date;
9 exception
10 when others then null;
11 end;
12
13 --
14
15 begin
16 l_date := to_date(par_str, 'mon dd yyyy');
17 return l_date;
18 exception
19 when others then null;
20 end;
21
22 --
23
24 begin
25 l_date := to_date(par_str, 'dd-mon-yyyy');
26 return l_date;
27 exception
28 when others then null;
29 end;
30
31 --
32
33 begin
34 l_date := to_date(par_str, 'month dd yyyy');
35 return l_date;
36 exception
37 when others then null;
38 end;
39
40 --
41
42 begin
43 l_date := to_date(par_str, 'dd/mm/yyyy');
44 return l_date;
45 exception
46 when others then null;
47 end;
48
49 return null;
50
51 exception
52 when others then
53 return null;
54 end f_date;
55 /
Function created.
Testing:
SQL> select actual, f_date(actual) as expected
2 from test;
ACTUAL EXPECTED
--------------- -----------
SEP-10-2017 10-SEP-2017
SEP 30 2018 30-SEP-2018
OFFICE OF SMALL
09-SEP-2009 09-SEP-2009
Not applicable
AUGUST 03 2017 03-AUG-2017
97/2015
09/09/2018 09-SEP-2018
8 rows selected.
SQL>
Possible problems: if actual = 09/10/12, what is what?
09 can be day, month or year
10 can also be day, month or year
12 can also be day, month or year
So, what is it?
09-OCT-2012
10-SEP-2012
12-OCT-2009
...

Answer 3

If you're sure about that you don't have any other type of the format for those values which can be convertible to a date value(eg.all of the data conform with this sample data set), then use the following code block in order to populate another table(t2) with the decent date values while displaying the rotten values such as
SQL> SET SERVEROUTPUT ON
SQL> DECLARE
dt DATE;
BEGIN
FOR c IN (SELECT * FROM t) LOOP
BEGIN
dt := TO_DATE(c.col, 'MON-DD-YYYY', 'NLS_DATE_LANGUAGE=ENGLISH');
INSERT INTO t2 VALUES(c.id,c.col);
EXCEPTION
WHEN OTHERS THEN
BEGIN
dt := TO_DATE(c.col, 'DD/MM/YYYY', 'NLS_DATE_LANGUAGE=ENGLISH');
INSERT INTO t2 VALUES(c.id,c.col);
EXCEPTION
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE(c.col || ' is not a valid date value');
END;
END;
END LOOP;
COMMIT;
END;
/
Demo