BigQuery converting to a different timezone - datetime

Question

I am storing data in unixtimestamp on google big query. However, when the user will ask for a report, she will need the filtering and grouping of data by her local timezone.
The data is stored in GMT. The user may wish to see the data in EST. The report may ask the data to be grouped by date.
I don't see the timezone conversion function here:
Does anyone know how I can do this in bigquery? i.e. how do i group by after converting the timestamp to a different timezone?

Answer 1

Standard SQL in BigQuery has built-in functions:
DATE(timestamp_expression, timezone)
TIME(timestamp, timezone)
DATETIME(timestamp_expression, timezone)
Example:
SELECT
original,
DATETIME(original, "America/Los_Angeles") as adjusted
FROM sometable;
+---------------------+---------------------+
| original | adjusted |
+---------------------+---------------------+
| 2008-12-25 05:30:00 | 2008-12-24 21:30:00 |
+---------------------+---------------------+
You can use standard IANA timezone names or offsets.

Answer 2

As of September 2016 BigQuery has adopted standard SQL and you can now just use the "DATE(timestamp, timezone)" function to offset for a timezone. You can reference their docs here:
BigQuery DATE docs

Answer 3

To those that stumble here:
How to convert a timestamp to another timezone?
Given that TIMESTAMP values, once constructed, are stored as UTC, and that TIMESTAMP does not have a constructor (TIMESTAMP, STRING), you can convert a timestamp to another time zone by transforming it first to a DATETIME and then constructing the new TIMESTAMP from the DATETIME in the new timezone:
SELECT TIMESTAMP(DATETIME(timestamp_field, '{timezone}'))
Example:
SELECT
input_tz,
input,
'America/Montreal' AS output_tz,
TIMESTAMP(DATETIME(input,'America/Montreal')) AS output
FROM (
SELECT 'US/Pacific' AS input_tz, TIMESTAMP(DATETIME(DATE(2021, 1, 1), TIME(16, 0, 0)), 'US/Pacific') AS input
UNION ALL
SELECT 'UTC' AS input_tz, TIMESTAMP(DATETIME(DATE(2021, 1, 1), TIME(16, 0, 0)), 'UTC') AS input
UNION ALL
SELECT 'Europe/Berlin' AS input_tz, TIMESTAMP(DATETIME(DATE(2021, 1, 1), TIME(16, 0, 0)), 'Europe/Berlin') AS input
) t
results in:
Row
input_tz
input
output_tz
output
1
US/Pacific
2021-01-02 00:00:00 UTC
America/Montreal
2021-01-01 19:00:00 UTC
2
UTC
2021-01-01 16:00:00 UTC
America/Montreal
2021-01-01 11:00:00 UTC
3
Europe/Berlin
2021-01-01 15:00:00 UTC
America/Montreal
2021-01-0110:00:00 UTC
How to strip time zone info from a DATETIME value?
DATETIME in BigQuery are time zone naive, such that they do not contain timezone info. This being said, if you have business knowledge that allows you to know the timezone of a DATETIME, you can strip that timezone offset by converting it to a TIMESTAMP with the known timezone:
SELECT TIMESTAMP(datetime_value, '{timezone}')
Given that the TIMESTAMP stores the value in UTC, you can then re-convert to DATETIME if that's your preferred method of storage, but now you'll know that your DATETIME is in UTC :)
Hopefully this can be helpful! :)

Answer 4

Your premise is right. If you group like this, then users who want EST or EDT will get incorrect date grouping:
GROUP BY UTC_USEC_TO_DAY(ts_field)
But as long as you figure out the offset that your user wants, you can still do the full calculation on the server. For example, if EST is 5 hours behind UTC then query like this:
GROUP BY UTC_USEC_TO_DAY(ts_field - (5*60*60*1000*1000000) )
Just parameterize the "5" to be the offset in hours, and you're all set. Here's a sample based on one of the sample data sets:
SELECT
COUNT(*) as the_count,
UTC_USEC_TO_DAY(timestamp * 1000000 - (5*60*60*1000*1000000) ) as the_day
FROM
[publicdata:samples.wikipedia]
WHERE
comment CONTAINS 'disaster'
and timestamp >= 1104537600
GROUP BY
the_day
ORDER BY
the_day
You can remove the offset to see how some edits move to different days.

Answer 5

To convert any TimeZone DateTime string to UTC, one could use PARSE_TIMESTAMP using the supported TIMESTAMP Formats in BigQuery.
For example to convert IST (Indian Standard Time) string to UTC, use the following:
SAFE.PARSE_TIMESTAMP("%a %b %d %T IST %Y", timeStamp_vendor, "Asia/Kolkata")
Here PARSE_TIMESTAMP parses the IST string to a UTC TIMESTAMP (not string). Adding SAFE as prefix takes care of errors/nulls etc.
To convert this to a readable string format in BigQuery, use FORMAT_TIMESTAMP as follows:
FORMAT_TIMESTAMP("%d-%b-%Y %T %Z", SAFE.PARSE_TIMESTAMP("%a %b %d %T IST %Y", timeStamp_vendor, "Asia/Kolkata"))
This example would take an IST string of the format Fri May 12 09:45:12 IST 2019 and convert it to 12-May-2019 04:15:12 UTC.
Replace IST with the required TimeZone and Asia/Kolkata with relevant Timezone name to achieve the conversion for your timezone

Answer 6

2016 update: Look answers below, BigQuery now provides timestamp and timezone methods.
You are right - BigQuery doesn't provide any timestamp conversion methods.
In this case, I suggest that you run your GROUP BY based on dimensions of the GMT/UTC timestamp field, and then convert and display the result in the local timezone in your code.

Answer 7

For me TIMESTAMP_SUB and TIMESTAMP_ADD functions did the job. When needed to convert timestamp from UTC to PST I used:
TIMESTAMP_SUB(`timestamp`, INTERVAL 8 HOUR)