Converting a SQL Server Timezone object `yyyy-mm-dd HH:MM;SS+HH` to a valid datetime (UTC)

Question

I have a string representation of datetime values which has an offset +03 I'm assuming this means +03 hours I most likely may be wrong.

This is a typical value in my table:

2015-05-15 21:35:19+03

there are only two unique values +3 or +2 I'm not sure what the source system is/was.

I wonder what the correct way to convert such an object is? my current method is to split the offset and convert the remainder to a datetime object and add the offset using dateadd

SELECT DATEADD(hour, CAST(value AS int)
          , CAST(REPLACE(dt, '+' + value, '') AS DATETIME2)) AS offset_val
, dt
FROM (

       VALUES ('2015-05-15 21:35:19+03')
            , ('2015-05-15 19:35:19+03')
) t(dt)
  CROSS APPLY (
                SELECT VALUE
                     , ROW_NUMBER() OVER (ORDER BY VALUE) AS seq
                FROM STRING_SPLIT(t.dt, '+')
) ch
WHERE
  seq = 1

---

+---------------------------+----------------------+
|offset_val                 |dt                    |
+---------------------------+----------------------+
|2015-05-16 00:35:19.0000000|2015-05-15 21:35:19+03|
|2015-05-15 22:35:19.0000000|2015-05-15 19:35:19+03|
+---------------------------+----------------------+

Answer 1

You got the offset the other way around, 21:35:19+03 is UTC+3 and it represents 18:35:19 in UTC.

That being said, your string representation parses just fine as datetimeoffset and you can then just convert it to UTC:

SELECT PARSE('2015-05-15 21:35:19+03' AS datetimeoffset USING 'en-us') AT TIME ZONE 'UTC'