Checking a specific date format in Oracle SQL using RegexLike - sql

Question

I am using oracle data integrator as an ETL tool to load data, there is one column which as a source comes in format YYYYMMDD for ex: 20190418. I want to query that table to identify all those records which do not fit 20190418 or YYYYMMDD format.
P.S. the column is in varchar2 datatype.
I already tried using something like this:
SELECT CASE WHEN NOT REGEXP_LIKE('20190418', '^\d{4}(0[1-9]|1[12])(0[1-9]|[12]\d|3[01])$') then '00000000' else '20190418' END FROM DUAL;
This seems to identify those illegal dates, but for example it didn't work for this one : '20181023'.
Can someone figure it out, I think I am missing some kind of pattern

Answer 1

I would propose a function rather than a regex, will be easier.
CREATE OR REPLACE FUNCTION Verify_date_number(inNumber IN NUMBER) RETURN VARCHAR2 AS
res DATE;
BEGIN
res := TO_DATE(inNumber, 'fxYYYYMMDD');
RETURN TO_CHAR(res, 'YYYYMMDD');
EXCEPTION
WHEN OTHERS THEN
RETURN '00000000';
END;
If you are running Oracle 12.2 then you can also use VALIDATE_CONVERSION
SELECT
CASE VALIDATE_CONVERSION('20190418' AS DATE, 'fxYYYYMMDD')
WHEN 1 THEN '20190418'
ELSE '00000000'
END
FROM dual;

Answer 2

Using PL/SQL maybe a better alternative
declare
v_date date;
begin
for c in
(
select '20190418' as date_str from dual union all
select '20191804' from dual union all
select '201904187' from dual
)
loop
begin
v_date := to_date(c.date_str,'yyyymmdd');
dbms_output.put_line(c.date_str);
exception when others then null;
end;
end loop;
end;
gives only the decently formatted data as output. In the above case, it's
20190418 only.
For 20191804, we would get ORA-01843: not a valid month
For 201904187, we would get ORA-01830: date format picture ends before converting entire input string
errors

Answer 3

you can try this one:
with tab as(
select '20190418' as dat from dual union all
select '20181023' as dat from dual union all
select '20181123' as dat from dual union all
select '20181223' as dat from dual union all
select '20181201' as dat from dual union all
select '20181209' as dat from dual union all
select '20181210' as dat from dual union all
select '20181229' as dat from dual union all
select '20181231' as dat from dual union all
select '20181232' as dat from dual union all
select '20181200' as dat from dual union all
select '20191418' as dat from dual
)
SELECT CASE WHEN NOT REGEXP_LIKE(dat, '^\d{4}(0[1-9]|(1[0-2]))(0[1-9]|[1-2][0-9]|3[0-1])$') then '00000000' else dat END as dat
FROM tab;
Result:
20190418
20181023
20181123
20181223
20181201
20181209
20181210
20181229
20181231
00000000
00000000
00000000