How to convert partial dates in Oracle SQL - sql

Question

I have 2 date columns in 2 diff tables that I need to compare, both varchar2 type. Both columns have partial and full dates based on the data.
T1:
ID Partial_date1
1 19-DEC-2016
2 06-MAY-2015
3 2016
4
5 AUG-2016
6 16-NOV-2015 00:00
7 01-JAN-2016
T2:
ID Partial_date2
1 09-JAN-2016
2 2016
3 SEP-2015
4
5 23-MAR-2016 00:00
6 15-MAY-2015
7
I want to search for all records that have full dates (as it is not possible to convert partial dates), to select only the records with full dates, I have used length >10. Here is the SQL I wrote but does not seem to be working.
select t1.id from t1, t2
where t1.id =t2.id
and length(t1.partial_date1)>10
and length(t2.partial_date2)>10
and to_date(t1.partial_date1,'DD-MON-YYYY') > to_date(t2.partial_date2,'DD-MON-YYYY')
I either get an error - ORA-01830: date format picture ends before converting entire input string
or literal does not match format string.
What am I doing wrong? how do I get the right results?

Answer 1

It seems you consider a date complete when the string starts with DD-MMM-YYYY. You can use REGEXP_LIKE to find such rows:
where regexp_like(partial_date, '^[[:digit:]]{2}-[[:upper:]]{3}-[[:digit:]]{4}')
(You may want to adjust the pattern according to your needs, e.g. replace [[:upper:]] with [[:alpha:]].)
In order to convert a date containing a textual month you should use TO_DATE with a language parameter:
to_date(partial_date, 'DD-MON-YYYY', 'NLS_DATE_LANGUAGE=AMERICAN')
A possible query:
select tt1.id
from
(
select
id,
to_date(substr(partial_date1, 1, 11), 'DD-MON-YYYY', 'NLS_DATE_LANGUAGE=AMERICAN')
as dt
from t1
where regexp_like(partial_date1, '^[[:digit:]]{2}-[[:upper:]]{3}-[[:digit:]]{4}')
) tt1
join
(
select
id,
to_date(substr(partial_date2, 1, 11), 'DD-MON-YYYY', 'NLS_DATE_LANGUAGE=AMERICAN')
as dt
from t2
where regexp_like(partial_date2, '^[[:digit:]]{2}-[[:upper:]]{3}-[[:digit:]]{4}')
) tt2 on tt2.id = tt1.id and tt2.dt < tt1.dt;
However, keep in mind that you are still dealing with strings. Conversion on "dates" like these would fail and crash your query:
30-FEB-2017
01-YAN-2017
99-XXX-9999
So depending on the data quality your best bet may be to write a PL/SQL function in order to catch conversion errors.

Answer 2

When you write condition in where clause oracle may use it as access predicate. And it function to_date(t1.partial_date1,'DD-MON-YYYY') is used to any row.
That's why you get an error.
I see two ways:
First way is use a subquery to get a shrunk dataset, substr only 10 symbols and then convert it
with t1(id,partial_date1) as
(
select 1,'19-DEC-2016' from dual union all
select 2,'06-MAY-2015' from dual union all
select 3, '2016' from dual union all
select 4,'' from dual union all
select 5,'AUG-2016' from dual union all
select 6,'16-NOV-2015 00:00' from dual union all
select 7, '01-JAN-2016' from dual
), t2(id,partial_date2) as
(
select 1,'09-JAN-2016' from dual union all
select 2,'2016' from dual union all
select 3,'SEP-2015' from dual union all
select 4,'' from dual union all
select 5,'23-MAR-2016 00:00' from dual union all
select 6,'15-MAY-2015' from dual union all
select 7,'' from dual
)
select *
from
(select
t1.id,
partial_date1,
partial_date2
from
t1, t2
where
t1.id =t2.id
and length(t1.partial_date1) > 10
and length(t2.partial_date2) > 10
and rownum > 0)
where
to_date(substr(partial_date1,1,10),'DD-MON-YYYY') > to_date(substr(partial_date2,1,10),'DD-MON-YYYY');
/
The second way is to explicitly convert any format to properly one
with t1(id,partial_date1) as (
select 1,'19-DEC-2016' from dual union all
select 2,'06-MAY-2015' from dual union all
select 3, '2016' from dual union all
select 4,'' from dual union all
select 5,'AUG-2016' from dual union all
select 6,'16-NOV-2015 00:00' from dual union all
select 7, '01-JAN-2016' from dual)
,t2(id,partial_date2) as (
select 1,'09-JAN-2016' from dual union all
select 2,'2016' from dual union all
select 3,'SEP-2015' from dual union all
select 4,'' from dual union all
select 5,'23-MAR-2016 00:00' from dual union all
select 6,'15-MAY-2015' from dual union all
select 7,'' from dual)
select * from(
select t1.id,
case
when regexp_like(t1.partial_date1,'\d{1,2}-\w{3}-\d{4} \d{1,2}:\d{2}') then to_date(t1.partial_date1,'dd-MON-yyyy HH24:MI')
when regexp_like(t1.partial_date1,'\d{1,2}-\w{3}-\d{4}') then to_date(t1.partial_date1,'dd-MON-yyyy')
when regexp_like(t1.partial_date1,'\w{3}-\d{4}') then to_date(t1.partial_date1,'MON-yyyy')
when regexp_like(t1.partial_date1,'\d{4}') then to_date(t1.partial_date1,'yyyy')
end as pd1,
case
when regexp_like(t2.partial_date2,'\d{1,2}-\w{3}-\d{4} \d{1,2}:\d{2}') then to_date(t2.partial_date2,'dd-MON-yyyy HH24:MI')
when regexp_like(t2.partial_date2,'\d{1,2}-\w{3}-\d{4}') then to_date(t2.partial_date2,'dd-MON-yyyy')
when regexp_like(t2.partial_date2,'\w{3}-\d{4}') then to_date(t2.partial_date2,'MON-yyyy')
when regexp_like(t2.partial_date2,'\d{4}') then to_date(t2.partial_date2,'yyyy')
end as pd2
from t1,t2
where t1.id = t2.id)
where pd1 > pd2
/

Answer 3

case
when PurchaseDate = '0' then NULL
when right(PurchaseDate, 4) = '0000' then convert(date, left(PurchaseDate,4) + '1231', 112)
when RIGHT(PurchaseDate, 2) = '00' then DATEADD(day,-1,DATEADD(month,cast(left(RIGHT(Purchasedate,4),2) AS INT),DATEADD(year,cast(LEFT(Purchasedate, 4) AS int)-1900,0)))
else convert(date, ltrim(rtrim(cast(PurchaseDate as varchar(50)))), 112)
end
Apologize. This is from my phone. This does a few things. It assumes different formats plus it counters for missing days and months.
Hope this helps.