to_Char(DATE) with time - sql

Question

I have a DB (Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production). In there is a table (Course) in which I have a Date column (start_dte). I want to format the output to a char so I used:
SELECT start_dte,
to_Char(start_dte) AS start_dte_2,
to_Char(start_dte,'DD.MM.YYYY') AS start_dte_3,
to_Char(start_dte,'DD.MM.YYYY HH24:MI:SS') AS start_dte_4,
to_Char(start_dte,'DD.MM.YYYY HH12:MI:SS') AS start_dte_5,
to_Char(start_dte,'DD.MM.YYYY HH.MI.SSXFF AM') AS start_dte_6,
to_Char(start_dte,'DD.MM.YYYY HH24:MI:SSxFF') AS start_dte_7,
to_Char(start_dte,'DD-MON-YYYY HH24:MI:SSxFF TZH:TZM') AS start_dte_8
FROM Course
The Results:
Number 6,7,8 give me
java.sql.SQLException: ORA-01821: date format not recognized
6 has the same format as:
SELECT value
FROM V$NLS_PARAMETERS
WHERE parameter = 'NLS_TIME_FORMAT'
7 and 8 are taken from the Oracle documentation but this is only for timestamps. So what i am missing? I know the actual datatype should be datetime but I only have read access to that DB. What i would actually like:
Or even better:

Answer 1

A DATE doesn't have any time zone information, so if you want to adjust the displayed time then you'll need to specify which time zone that date nominally represents, and which time zone you want to convert it to.
An an example, if your stored date represents UTC and you want to see the equivalent local time in Paris, you can state that the stored time is UTC by casting it as a plain timestamp and passing that into the from_tz() function; and then specify the target timezone with at:
-- CTE for your sample data
with course (start_dte) as (
select cast(timestamp '2018-10-17 14:00:00' as date) from dual
)
-- actual query
select from_tz(cast(start_dte as timestamp), 'UTC')
at time zone 'Europe/Paris' as start_timestamp_tz
from course;
START_TIMESTAMP_TZ
------------------------------------------
2018-10-17 16:00:00.000000000 EUROPE/PARIS
Since you're querying this via JDBC you probably want to retrieve that as its native data type, and then choose how to display it locally. (But you could presumably query it as a date and adjust it in Java too...)
If you want to convert it to a string on the DB side, though, just use the format model you already used:
select to_char(from_tz(cast(start_dte as timestamp), 'UTC')
at time zone 'Europe/Paris', 'DD.MM.YYYY HH24:MI') as start_date
from course;
START_DATE
----------------
17.10.2018 16:00
Getting it into two fields is also simple, and if you don't want to repeat the conversion you can use a CTE or an inline view:
select to_char(start_timestamp_tz, 'DD.MM.YYYY') as start_date,
to_char(start_timestamp_tz, 'HH24:MI') as start_time
from (
select from_tz(cast(start_dte as timestamp), 'UTC')
at time zone 'Europe/Paris' as start_timestamp_tz
from course
);
START_DATE START_TIME
---------- ----------
17.10.2018 16:00
But it sounds like Java should be doing that conversion to strings for display.

Answer 2

What i would actually like:
| START_DATE |
|------------------|
| 17.10.2018 16:00 |
Or even better:
| START_DATE | START_TIME |
|------------|------------|
| 17.10.2018 | 16:00 |
Use:
SELECT to_Char(start_dte,'DD.MM.YYYY') AS start_date,
to_Char(start_dte,'HH24:MI') AS start_time
FROM Course
If your data is stored in the table in one time zone (i.e. UTC) and you want it in another time zone then use:
CAST( date_value AS TIMESTAMP ) to convert it from a DATE data type to a TIMESTAMP data type.
FROM_TZ( timestamp_value, timezone_string ) to convert it from a TIMESTAMP data type to a TIMESTAMP WITH TIME ZONE data type at the given time zone.
timestamp_with_timezone_value AT TIME ZONE timezone_string to convert it from one time zone to another time zone.
Like this:
SELECT TO_CHAR(
FROM_TZ( CAST( start_dte AS TIMESTAMP ), 'UTC' ) AT TIME ZONE 'Europe/Berlin',
'DD.MM.YYYY'
) AS start_date,
TO_CHAR(
FROM_TZ( CAST( start_dte AS TIMESTAMP ), 'UTC' ) AT TIME ZONE 'Europe/Berlin',
'HH24:MI'
) AS start_time
FROM Course

Answer 3

start_dte is a DATE value.
DATE does neither have fractional seconds (i.e. XFF) nor time zone information (i.e. TZH:TZM)
Use TIMESTAMP WITH TIME ZONE is you like to get such output.