Convert varchar into datetime in oracle - sql

Question

My datetime is saved in database as varchar in "o" format.
Example:
2020-10-08T06:58:54.0000000+02:00
What is the appropriate format for this kind of data?
I want convert it to datetime.

Answer 1

Fix your data model! Do not store dates as strings; this is inefficient (you need to convert the string to a date whenever you want to perform artihmetic operation), and unsafe (you cannot guarantee that the values are valid dates).
As for your question: it depends the datatype you want to convert that string to. Assuming that you want timestamp with time zone, which seems like the most relevant option here (it allows fractional seconds and a time zone):
select to_timestamp_tz(
'2020-10-08T06:58:54.0000000+02:00',
'yyyy-mm-dd"T"hh24:mi:ss.ff tzh:tzm'
) as myts
from dual
This returns this timestamp with time zone:
08-OCT-20 06.58.54.000000000 +02:00

Answer 2

Do NOT naively convert date-time values with a time zone to a date-time and ignore the time zone if you wish comparisons of those date-time-timezone values to still be accurate.
Your value has a time zone so the most natural method of storing the data would be TIMESTAMP WITH TIME ZONE and to convert it you can use:
TO_TIMESTAMP_TZ( your_column, 'YYYY-MM-DD"T"HH24:MI:SS.FF7TZH:TZM' )
However, if you want the value as a DATE data type then this data type does not support time zones and you should convert all the values to a common time zone (typically this would be the UTC time zone) using:
CAST(
TO_TIMESTAMP_TZ( your_column, 'YYYY-MM-DD"T"HH24:MI:SS.FF7TZH:TZM' )
AT TIME ZONE 'UTC'
AS DATE
)
If you do not use a common time zone then you will find that you can compare values and draw incorrect comparisons.
For example:
SELECT CASE
WHEN TO_TIMESTAMP_TZ( '2020-10-08T06:58:54.0000000+00:00', 'YYYY-MM-DD"T"HH24:MI:SS.FF7TZH:TZM' )
< TO_TIMESTAMP_TZ( '2020-10-08T07:58:54.0000000+02:00', 'YYYY-MM-DD"T"HH24:MI:SS.FF7TZH:TZM' )
THEN 1
ELSE 0
END AS comparison
FROM DUAL
and
SELECT CASE
WHEN CAST(
TO_TIMESTAMP_TZ( '2020-10-08T06:58:54.0000000+00:00', 'YYYY-MM-DD"T"HH24:MI:SS.FF7TZH:TZM' )
AT TIME ZONE 'UTC'
AS DATE
)
<
CAST(
TO_TIMESTAMP_TZ( '2020-10-08T07:58:54.0000000+02:00', 'YYYY-MM-DD"T"HH24:MI:SS.FF7TZH:TZM' )
AT TIME ZONE 'UTC'
AS DATE
)
THEN 1
ELSE 0
END AS comparison
FROM DUAL
Both output:
| COMPARISON |
| ---------: |
| 0 |
However, naively using TO_DATE:
SELECT CASE
WHEN TO_DATE( '2020-10-08T06:58:54.0000000+00:00', 'YYYY-MM-DD"T"HH24:MI:SS##############' )
< TO_DATE( '2020-10-08T07:58:54.0000000+02:00', 'YYYY-MM-DD"T"HH24:MI:SS##############' )
THEN 1
ELSE 0
END AS comparison
FROM DUAL
Outputs:
| COMPARISON |
| ---------: |
| 1 |
db<>fiddle here

Answer 3

If your column is varchar2 and dates are stores in the string then you can use TO_DATE to convert it to date as follows:
SQL> SELECT TO_DATE('2020-10-08T06:58:54.0000000+02:00', 'YYYY-MM-DD"T"HH24:MI:SS.#############')
2 FROM DUAL;
TO_DATE('2020-10-08T
--------------------
08-oct-2020 06:58:54
SQL>
# is used to skip the character. I am ignoring the timezone and millisecond part as while converting to Date(&Time) it is not needed.