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Timestamp functions | BigQuery | Google Cloud

GoogleSQL for BigQuery supports the following timestamp functions.

IMPORTANT: Before working with these functions, you need to understand the difference between the formats in which timestamps are stored and displayed, and how time zones are used for the conversion between these formats. To learn more, see How time zones work with timestamp functions.

NOTE: These functions return a runtime error if overflow occurs; result values are bounded by the defined DATE range and TIMESTAMP range.

Function list Name Summary CURRENT_TIMESTAMP Returns the current date and time as a TIMESTAMP object. EXTRACT Extracts part of a TIMESTAMP value. FORMAT_TIMESTAMP Formats a TIMESTAMP value according to the specified format string. GENERATE_TIMESTAMP_ARRAY Generates an array of timestamps in a range.
For more information, see Array functions. PARSE_TIMESTAMP Converts a STRING value to a TIMESTAMP value. STRING (Timestamp) Converts a TIMESTAMP value to a STRING value. TIMESTAMP Constructs a TIMESTAMP value. TIMESTAMP_ADD Adds a specified time interval to a TIMESTAMP value. TIMESTAMP_DIFF Gets the number of unit boundaries between two TIMESTAMP values at a particular time granularity. TIMESTAMP_MICROS Converts the number of microseconds since 1970-01-01 00:00:00 UTC to a TIMESTAMP. TIMESTAMP_MILLIS Converts the number of milliseconds since 1970-01-01 00:00:00 UTC to a TIMESTAMP. TIMESTAMP_SECONDS Converts the number of seconds since 1970-01-01 00:00:00 UTC to a TIMESTAMP. TIMESTAMP_SUB Subtracts a specified time interval from a TIMESTAMP value. TIMESTAMP_TRUNC Truncates a TIMESTAMP or DATETIME value at a particular granularity. UNIX_MICROS Converts a TIMESTAMP value to the number of microseconds since 1970-01-01 00:00:00 UTC. UNIX_MILLIS Converts a TIMESTAMP value to the number of milliseconds since 1970-01-01 00:00:00 UTC. UNIX_SECONDS Converts a TIMESTAMP value to the number of seconds since 1970-01-01 00:00:00 UTC. CURRENT_TIMESTAMP

CURRENT_TIMESTAMP()

CURRENT_TIMESTAMP

Description

Returns the current date and time as a timestamp object. The timestamp is continuous, non-ambiguous, has exactly 60 seconds per minute and doesn't repeat values over the leap second. Parentheses are optional.

This function handles leap seconds by smearing them across a window of 20 hours around the inserted leap second.

The current timestamp value is set at the start of the query statement that contains this function. All invocations of CURRENT_TIMESTAMP() within a query statement yield the same value.

Supported Input Types

Not applicable

Result Data Type

TIMESTAMP

Examples

SELECT CURRENT_TIMESTAMP() AS now;

/*--------------------------------*
 | now                            |
 +--------------------------------+
 | 2020-06-02 23:57:12.120174 UTC |
 *--------------------------------*/

EXTRACT(part FROM timestamp_expression [AT TIME ZONE time_zone])

Description

Returns a value that corresponds to the specified part from a supplied timestamp_expression. This function supports an optional time_zone parameter. See Time zone definitions for information on how to specify a time zone.

Allowed part values are:

MICROSECOND
MILLISECOND
SECOND
MINUTE
HOUR
DAYOFWEEK: Returns values in the range [1,7] with Sunday as the first day of of the week.
DAY
DAYOFYEAR
WEEK: Returns the week number of the date in the range [0, 53]. Weeks begin with Sunday, and dates prior to the first Sunday of the year are in week 0.
WEEK(<WEEKDAY>): Returns the week number of timestamp_expression in the range [0, 53]. Weeks begin on WEEKDAY. datetimes prior to the first WEEKDAY of the year are in week 0. Valid values for WEEKDAY are SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, and SATURDAY.
ISOWEEK: Returns the ISO 8601 week number of the datetime_expression. ISOWEEKs begin on Monday. Return values are in the range [1, 53]. The first ISOWEEK of each ISO year begins on the Monday before the first Thursday of the Gregorian calendar year.
MONTH
QUARTER
YEAR
ISOYEAR: Returns the ISO 8601 week-numbering year, which is the Gregorian calendar year containing the Thursday of the week to which date_expression belongs.
DATE
DATETIME
TIME

Returned values truncate lower order time periods. For example, when extracting seconds, EXTRACT truncates the millisecond and microsecond values.

Return Data Type

INT64, except in the following cases:

If part is DATE, the function returns a DATE object.

Examples

In the following example, EXTRACT returns a value corresponding to the DAY time part.

SELECT
  EXTRACT(
    DAY
    FROM TIMESTAMP('2008-12-25 05:30:00+00') AT TIME ZONE 'UTC')
    AS the_day_utc,
  EXTRACT(
    DAY
    FROM TIMESTAMP('2008-12-25 05:30:00+00') AT TIME ZONE 'America/Los_Angeles')
    AS the_day_california

/*-------------+--------------------*
 | the_day_utc | the_day_california |
 +-------------+--------------------+
 | 25          | 24                 |
 *-------------+--------------------*/

In the following examples, EXTRACT returns values corresponding to different time parts from a column of type TIMESTAMP.

SELECT
  EXTRACT(ISOYEAR FROM TIMESTAMP("2005-01-03 12:34:56+00")) AS isoyear,
  EXTRACT(ISOWEEK FROM TIMESTAMP("2005-01-03 12:34:56+00")) AS isoweek,
  EXTRACT(YEAR FROM TIMESTAMP("2005-01-03 12:34:56+00")) AS year,
  EXTRACT(WEEK FROM TIMESTAMP("2005-01-03 12:34:56+00")) AS week

-- Display of results may differ, depending upon the environment and
-- time zone where this query was executed.
/*---------+---------+------+------*
 | isoyear | isoweek | year | week |
 +---------+---------+------+------+
 | 2005    | 1       | 2005 | 1    |
 *---------+---------+------+------*/

SELECT
  TIMESTAMP("2007-12-31 12:00:00+00") AS timestamp_value,
  EXTRACT(ISOYEAR FROM TIMESTAMP("2007-12-31 12:00:00+00")) AS isoyear,
  EXTRACT(ISOWEEK FROM TIMESTAMP("2007-12-31 12:00:00+00")) AS isoweek,
  EXTRACT(YEAR FROM TIMESTAMP("2007-12-31 12:00:00+00")) AS year,
  EXTRACT(WEEK FROM TIMESTAMP("2007-12-31 12:00:00+00")) AS week

-- Display of results may differ, depending upon the environment and time zone
-- where this query was executed.
/*---------+---------+------+------*
 | isoyear | isoweek | year | week |
 +---------+---------+------+------+
 | 2008    | 1       | 2007 | 52    |
 *---------+---------+------+------*/

SELECT
  TIMESTAMP("2009-01-01 12:00:00+00") AS timestamp_value,
  EXTRACT(ISOYEAR FROM TIMESTAMP("2009-01-01 12:00:00+00")) AS isoyear,
  EXTRACT(ISOWEEK FROM TIMESTAMP("2009-01-01 12:00:00+00")) AS isoweek,
  EXTRACT(YEAR FROM TIMESTAMP("2009-01-01 12:00:00+00")) AS year,
  EXTRACT(WEEK FROM TIMESTAMP("2009-01-01 12:00:00+00")) AS week

-- Display of results may differ, depending upon the environment and time zone
-- where this query was executed.
/*---------+---------+------+------*
 | isoyear | isoweek | year | week |
 +---------+---------+------+------+
 | 2009    | 1       | 2009 | 0    |
 *---------+---------+------+------*/

SELECT
  TIMESTAMP("2009-12-31 12:00:00+00") AS timestamp_value,
  EXTRACT(ISOYEAR FROM TIMESTAMP("2009-12-31 12:00:00+00")) AS isoyear,
  EXTRACT(ISOWEEK FROM TIMESTAMP("2009-12-31 12:00:00+00")) AS isoweek,
  EXTRACT(YEAR FROM TIMESTAMP("2009-12-31 12:00:00+00")) AS year,
  EXTRACT(WEEK FROM TIMESTAMP("2009-12-31 12:00:00+00")) AS week

-- Display of results may differ, depending upon the environment and time zone
-- where this query was executed.
/*---------+---------+------+------*
 | isoyear | isoweek | year | week |
 +---------+---------+------+------+
 | 2009    | 53      | 2009 | 52   |
 *---------+---------+------+------*/

SELECT
  TIMESTAMP("2017-01-02 12:00:00+00") AS timestamp_value,
  EXTRACT(ISOYEAR FROM TIMESTAMP("2017-01-02 12:00:00+00")) AS isoyear,
  EXTRACT(ISOWEEK FROM TIMESTAMP("2017-01-02 12:00:00+00")) AS isoweek,
  EXTRACT(YEAR FROM TIMESTAMP("2017-01-02 12:00:00+00")) AS year,
  EXTRACT(WEEK FROM TIMESTAMP("2017-01-02 12:00:00+00")) AS week

-- Display of results may differ, depending upon the environment and time zone
-- where this query was executed.
/*---------+---------+------+------*
 | isoyear | isoweek | year | week |
 +---------+---------+------+------+
 | 2017    | 1       | 2017 | 1    |
 *---------+---------+------+------*/

SELECT
  TIMESTAMP("2017-05-26 12:00:00+00") AS timestamp_value,
  EXTRACT(ISOYEAR FROM TIMESTAMP("2017-05-26 12:00:00+00")) AS isoyear,
  EXTRACT(ISOWEEK FROM TIMESTAMP("2017-05-26 12:00:00+00")) AS isoweek,
  EXTRACT(YEAR FROM TIMESTAMP("2017-05-26 12:00:00+00")) AS year,
  EXTRACT(WEEK FROM TIMESTAMP("2017-05-26 12:00:00+00")) AS week

-- Display of results may differ, depending upon the environment and time zone
-- where this query was executed.
/*---------+---------+------+------*
 | isoyear | isoweek | year | week |
 +---------+---------+------+------+
 | 2017    | 21      | 2017 | 21   |
 *---------+---------+------+------*/

In the following example, timestamp_expression falls on a Monday. EXTRACT calculates the first column using weeks that begin on Sunday, and it calculates the second column using weeks that begin on Monday.

SELECT
  EXTRACT(WEEK(SUNDAY) FROM TIMESTAMP("2017-11-06 00:00:00+00")) AS week_sunday,
  EXTRACT(WEEK(MONDAY) FROM TIMESTAMP("2017-11-06 00:00:00+00")) AS week_monday

-- Display of results may differ, depending upon the environment and time zone
-- where this query was executed.
/*-------------+---------------*
 | week_sunday | week_monday   |
 +-------------+---------------+
 | 45          | 44            |
 *-------------+---------------*/

FORMAT_TIMESTAMP

FORMAT_TIMESTAMP(format_string, timestamp_expr[, time_zone])

Description

Formats a TIMESTAMP value according to the specified format string.

Definitions

format_string: A STRING value that contains the format elements to use with timestamp_expr.
timestamp_expr: A TIMESTAMP value that represents the timestamp to format.
time_zone: A STRING value that represents a time zone. For more information about how to use a time zone with a timestamp, see Time zone definitions.

Return Data Type

STRING

Examples

SELECT FORMAT_TIMESTAMP("%c", TIMESTAMP "2050-12-25 15:30:55+00", "UTC")
  AS formatted;

/*--------------------------*
 | formatted                |
 +--------------------------+
 | Sun Dec 25 15:30:55 2050 |
 *--------------------------*/

SELECT FORMAT_TIMESTAMP("%b-%d-%Y", TIMESTAMP "2050-12-25 15:30:55+00")
  AS formatted;

/*-------------*
 | formatted   |
 +-------------+
 | Dec-25-2050 |
 *-------------*/

SELECT FORMAT_TIMESTAMP("%b %Y", TIMESTAMP "2050-12-25 15:30:55+00")
  AS formatted;

/*-------------*
 | formatted   |
 +-------------+
 | Dec 2050    |
 *-------------*/

SELECT FORMAT_TIMESTAMP("%Y-%m-%dT%H:%M:%SZ", TIMESTAMP "2050-12-25 15:30:55", "UTC")
  AS formatted;

/*+---------------------*
 |      formatted       |
 +----------------------+
 | 2050-12-25T15:30:55Z |
 *----------------------*/

PARSE_TIMESTAMP

PARSE_TIMESTAMP(format_string, timestamp_string[, time_zone])

Description

Converts a STRING value to a TIMESTAMP value.

Definitions

format_string: A STRING value that contains the format elements to use with timestamp_string.
timestamp_string: A STRING value that represents the timestamp to parse.
time_zone: A STRING value that represents a time zone. For more information about how to use a time zone with a timestamp, see Time zone definitions.

Details

Each element in timestamp_string must have a corresponding element in format_string. The location of each element in format_string must match the location of each element in timestamp_string.

-- This works because elements on both sides match.
SELECT PARSE_TIMESTAMP("%a %b %e %I:%M:%S %Y", "Thu Dec 25 07:30:00 2008");

-- This produces an error because the year element is in different locations.
SELECT PARSE_TIMESTAMP("%a %b %e %Y %I:%M:%S", "Thu Dec 25 07:30:00 2008");

-- This produces an error because one of the year elements is missing.
SELECT PARSE_TIMESTAMP("%a %b %e %I:%M:%S", "Thu Dec 25 07:30:00 2008");

-- This works because %c can find all matching elements in timestamp_string.
SELECT PARSE_TIMESTAMP("%c", "Thu Dec 25 07:30:00 2008");

The format string fully supports most format elements, except for %P.

The following additional considerations apply when using the PARSE_TIMESTAMP function:

Unspecified fields. Any unspecified field is initialized from 1970-01-01 00:00:00.0. This initialization value uses the time zone specified by the function's time zone argument, if present. If not, the initialization value uses the default time zone, UTC. For instance, if the year is unspecified then it defaults to 1970, and so on.
Case insensitivity. Names, such as Monday, February, and so on, are case insensitive.
Whitespace. One or more consecutive white spaces in the format string matches zero or more consecutive white spaces in the timestamp string. In addition, leading and trailing white spaces in the timestamp string are always allowed, even if they aren't in the format string.
Format precedence. When two (or more) format elements have overlapping information (for example both %F and %Y affect the year), the last one generally overrides any earlier ones, with some exceptions (see the descriptions of %s, %C, and %y).
Format divergence. %p can be used with am, AM, pm, and PM.
Mixed ISO and non-ISO elements. The ISO format elements are %G, %g, %J, and %V. When these ISO elements are used together with other non-ISO elements, the ISO elements are ignored, resulting in different values. For example, the function arguments ('%g %J', '8405') return a value with the year 1984, whereas the arguments ('%g %j', '8405') return a value with the year 1970 because the ISO element %g is ignored.
Numeric values after %G input values. Any input string value that corresponds to the %G format element requires a whitespace or non-digit character as a separator from numeric values that follow. This is a known issue in GoogleSQL. For example, the function arguments ('%G %V','2020 50') or ('%G-%V','2020-50') work, but not ('%G%V','202050'). For input values before the corresponding %G value, no separator is needed. For example, the arguments ('%V%G','502020') work. The separator after the %G values identifies the end of the specified ISO year value so that the function can parse properly.

Return Data Type

TIMESTAMP

Example

SELECT PARSE_TIMESTAMP("%c", "Thu Dec 25 07:30:00 2008") AS parsed;

-- Display of results may differ, depending upon the environment and time zone where this query was executed.
/*-------------------------*
 | parsed                  |
 +-------------------------+
 | 2008-12-25 07:30:00 UTC |
 *-------------------------*/

STRING

STRING(timestamp_expression[, time_zone])

Description

Converts a timestamp to a string. Supports an optional parameter to specify a time zone. See Time zone definitions for information on how to specify a time zone.

Return Data Type

STRING

Example

SELECT STRING(TIMESTAMP "2008-12-25 15:30:00+00", "UTC") AS string;

/*-------------------------------*
 | string                        |
 +-------------------------------+
 | 2008-12-25 15:30:00+00        |
 *-------------------------------*/

TIMESTAMP

TIMESTAMP(string_expression[, time_zone])
TIMESTAMP(date_expression[, time_zone])
TIMESTAMP(datetime_expression[, time_zone])

Description

string_expression[, time_zone]: Converts a string to a timestamp. string_expression must include a timestamp literal. If string_expression includes a time zone in the timestamp literal, don't include an explicit time_zone argument.
date_expression[, time_zone]: Converts a date to a timestamp. The value returned is the earliest timestamp that falls within the given date.
datetime_expression[, time_zone]: Converts a datetime to a timestamp.

This function supports an optional parameter to specify a time zone. If no time zone is specified, the default time zone, UTC, is used.

Return Data Type

TIMESTAMP

Examples

SELECT TIMESTAMP("2008-12-25 15:30:00+00") AS timestamp_str;

-- Display of results may differ, depending upon the environment and time zone where this query was executed.
/*-------------------------*
 | timestamp_str           |
 +-------------------------+
 | 2008-12-25 15:30:00 UTC |
 *-------------------------*/

SELECT TIMESTAMP("2008-12-25 15:30:00", "America/Los_Angeles") AS timestamp_str;

-- Display of results may differ, depending upon the environment and time zone where this query was executed.
/*-------------------------*
 | timestamp_str           |
 +-------------------------+
 | 2008-12-25 23:30:00 UTC |
 *-------------------------*/

SELECT TIMESTAMP("2008-12-25 15:30:00 UTC") AS timestamp_str;

-- Display of results may differ, depending upon the environment and time zone where this query was executed.
/*-------------------------*
 | timestamp_str           |
 +-------------------------+
 | 2008-12-25 15:30:00 UTC |
 *-------------------------*/

SELECT TIMESTAMP(DATETIME "2008-12-25 15:30:00") AS timestamp_datetime;

-- Display of results may differ, depending upon the environment and time zone where this query was executed.
/*-------------------------*
 | timestamp_datetime      |
 +-------------------------+
 | 2008-12-25 15:30:00 UTC |
 *-------------------------*/

SELECT TIMESTAMP(DATE "2008-12-25") AS timestamp_date;

-- Display of results may differ, depending upon the environment and time zone where this query was executed.
/*-------------------------*
 | timestamp_date          |
 +-------------------------+
 | 2008-12-25 00:00:00 UTC |
 *-------------------------*/

TIMESTAMP_ADD

TIMESTAMP_ADD(timestamp_expression, INTERVAL int64_expression date_part)

Description

Adds int64_expression units of date_part to the timestamp, independent of any time zone.

TIMESTAMP_ADD supports the following values for date_part:

MICROSECOND
MILLISECOND
SECOND
MINUTE
HOUR. Equivalent to 60 MINUTE parts.
DAY. Equivalent to 24 HOUR parts.

Return Data Types

TIMESTAMP

Example

SELECT
  TIMESTAMP("2008-12-25 15:30:00+00") AS original,
  TIMESTAMP_ADD(TIMESTAMP "2008-12-25 15:30:00+00", INTERVAL 10 MINUTE) AS later;

-- Display of results may differ, depending upon the environment and time zone where this query was executed.
/*-------------------------+-------------------------*
 | original                | later                   |
 +-------------------------+-------------------------+
 | 2008-12-25 15:30:00 UTC | 2008-12-25 15:40:00 UTC |
 *-------------------------+-------------------------*/

TIMESTAMP_DIFF

TIMESTAMP_DIFF(end_timestamp, start_timestamp, granularity)

Description

Gets the number of unit boundaries between two TIMESTAMP values (end_timestamp - start_timestamp) at a particular time granularity.

Definitions

start_timestamp: The starting TIMESTAMP value.
end_timestamp: The ending TIMESTAMP value.
granularity: The timestamp part that represents the granularity. If you passed in TIMESTAMP values for the first arguments, granularity can be:
- MICROSECOND
- MILLISECOND
- SECOND
- MINUTE
- HOUR. Equivalent to 60 MINUTEs.
- DAY. Equivalent to 24 HOURs.

Details

If end_timestamp is earlier than start_timestamp, the output is negative. Produces an error if the computation overflows, such as if the difference in microseconds between the two TIMESTAMP values overflows.

Note: The behavior of the this function follows the type of arguments passed in. For example, TIMESTAMP_DIFF(DATE, DATE, PART) behaves like DATE_DIFF(DATE, DATE, PART).

Return Data Type

INT64

Example

SELECT
  TIMESTAMP("2010-07-07 10:20:00+00") AS later_timestamp,
  TIMESTAMP("2008-12-25 15:30:00+00") AS earlier_timestamp,
  TIMESTAMP_DIFF(TIMESTAMP "2010-07-07 10:20:00+00", TIMESTAMP "2008-12-25 15:30:00+00", HOUR) AS hours;

-- Display of results may differ, depending upon the environment and time zone where this query was executed.
/*-------------------------+-------------------------+-------*
 | later_timestamp         | earlier_timestamp       | hours |
 +-------------------------+-------------------------+-------+
 | 2010-07-07 10:20:00 UTC | 2008-12-25 15:30:00 UTC | 13410 |
 *-------------------------+-------------------------+-------*/

In the following example, the first timestamp occurs before the second timestamp, resulting in a negative output.

SELECT TIMESTAMP_DIFF(TIMESTAMP "2018-08-14", TIMESTAMP "2018-10-14", DAY) AS negative_diff;

/*---------------*
 | negative_diff |
 +---------------+
 | -61           |
 *---------------*/

In this example, the result is 0 because only the number of whole specified HOUR intervals are included.

SELECT TIMESTAMP_DIFF("2001-02-01 01:00:00", "2001-02-01 00:00:01", HOUR) AS diff;

/*---------------*
 | diff          |
 +---------------+
 | 0             |
 *---------------*/

TIMESTAMP_MICROS

TIMESTAMP_MICROS(int64_expression)

Description

Interprets int64_expression as the number of microseconds since 1970-01-01 00:00:00 UTC and returns a timestamp.

Return Data Type

TIMESTAMP

Example

SELECT TIMESTAMP_MICROS(1230219000000000) AS timestamp_value;

-- Display of results may differ, depending upon the environment and time zone where this query was executed.
/*-------------------------*
 | timestamp_value         |
 +-------------------------+
 | 2008-12-25 15:30:00 UTC |
 *-------------------------*/

TIMESTAMP_MILLIS

TIMESTAMP_MILLIS(int64_expression)

Description

Interprets int64_expression as the number of milliseconds since 1970-01-01 00:00:00 UTC and returns a timestamp.

Return Data Type

TIMESTAMP

Example

SELECT TIMESTAMP_MILLIS(1230219000000) AS timestamp_value;

-- Display of results may differ, depending upon the environment and time zone where this query was executed.
/*-------------------------*
 | timestamp_value         |
 +-------------------------+
 | 2008-12-25 15:30:00 UTC |
 *-------------------------*/

TIMESTAMP_SECONDS

TIMESTAMP_SECONDS(int64_expression)

Description

Interprets int64_expression as the number of seconds since 1970-01-01 00:00:00 UTC and returns a timestamp.

Return Data Type

TIMESTAMP

Example

SELECT TIMESTAMP_SECONDS(1230219000) AS timestamp_value;

-- Display of results may differ, depending upon the environment and time zone where this query was executed.
/*-------------------------*
 | timestamp_value         |
 +-------------------------+
 | 2008-12-25 15:30:00 UTC |
 *-------------------------*/

TIMESTAMP_SUB

TIMESTAMP_SUB(timestamp_expression, INTERVAL int64_expression date_part)

Description

Subtracts int64_expression units of date_part from the timestamp, independent of any time zone.

TIMESTAMP_SUB supports the following values for date_part:

MICROSECOND
MILLISECOND
SECOND
MINUTE
HOUR. Equivalent to 60 MINUTE parts.
DAY. Equivalent to 24 HOUR parts.

Return Data Type

TIMESTAMP

Example

SELECT
  TIMESTAMP("2008-12-25 15:30:00+00") AS original,
  TIMESTAMP_SUB(TIMESTAMP "2008-12-25 15:30:00+00", INTERVAL 10 MINUTE) AS earlier;

-- Display of results may differ, depending upon the environment and time zone where this query was executed.
/*-------------------------+-------------------------*
 | original                | earlier                 |
 +-------------------------+-------------------------+
 | 2008-12-25 15:30:00 UTC | 2008-12-25 15:20:00 UTC |
 *-------------------------+-------------------------*/

TIMESTAMP_TRUNC

TIMESTAMP_TRUNC(timestamp_value, timestamp_granularity[, time_zone])

TIMESTAMP_TRUNC(datetime_value, datetime_granularity)

Description

Truncates a TIMESTAMP or DATETIME value at a particular granularity.

Definitions

timestamp_value: A TIMESTAMP value to truncate.
timestamp_granularity: The truncation granularity for a TIMESTAMP value. Date granularities and time granularities can be used.
time_zone: A time zone to use with the TIMESTAMP value. Time zone parts can be used. Use this argument if you want to use a time zone other than the default time zone, UTC, as part of the truncate operation.
Note: When truncating a timestamp to MINUTE or HOUR parts, this function determines the civil time of the timestamp in the specified (or default) time zone and subtracts the minutes and seconds (when truncating to HOUR) or the seconds (when truncating to MINUTE) from that timestamp. While this provides intuitive results in most cases, the result is non-intuitive near daylight savings transitions that aren't hour-aligned.
datetime_value: A DATETIME value to truncate.
datetime_granularity: The truncation granularity for a DATETIME value. Date granularities and time granularities can be used.

Date granularity definitions

DAY: The day in the Gregorian calendar year that contains the value to truncate.
WEEK: The first day in the week that contains the value to truncate. Weeks begin on Sundays. WEEK is equivalent to WEEK(SUNDAY).
WEEK(WEEKDAY): The first day in the week that contains the value to truncate. Weeks begin on WEEKDAY. WEEKDAY must be one of the following: SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, or SATURDAY.
ISOWEEK: The first day in the ISO 8601 week that contains the value to truncate. The ISO week begins on Monday. The first ISO week of each ISO year contains the first Thursday of the corresponding Gregorian calendar year.
MONTH: The first day in the month that contains the value to truncate.
QUARTER: The first day in the quarter that contains the value to truncate.
YEAR: The first day in the year that contains the value to truncate.
ISOYEAR: The first day in the ISO 8601 week-numbering year that contains the value to truncate. The ISO year is the Monday of the first week where Thursday belongs to the corresponding Gregorian calendar year.

Time granularity definitions

MICROSECOND: If used, nothing is truncated from the value.
MILLISECOND: The nearest lesser than or equal millisecond.
SECOND: The nearest lesser than or equal second.
MINUTE: The nearest lesser than or equal minute.
HOUR: The nearest lesser than or equal hour.

Time zone part definitions

MINUTE
HOUR
DAY
WEEK
WEEK(<WEEKDAY>)
ISOWEEK
MONTH
QUARTER
YEAR
ISOYEAR

Details

The resulting value is always rounded to the beginning of granularity.

Return Data Type

The same data type as the first argument passed into this function.

Examples

SELECT
  TIMESTAMP_TRUNC(TIMESTAMP "2008-12-25 15:30:00+00", DAY, "UTC") AS utc,
  TIMESTAMP_TRUNC(TIMESTAMP "2008-12-25 15:30:00+00", DAY, "America/Los_Angeles") AS la;

-- Display of results may differ, depending upon the environment and time zone where this query was executed.
/*-------------------------+-------------------------*
 | utc                     | la                      |
 +-------------------------+-------------------------+
 | 2008-12-25 00:00:00 UTC | 2008-12-25 08:00:00 UTC |
 *-------------------------+-------------------------*/

In the following example, timestamp_expression has a time zone offset of +12. The first column shows the timestamp_expression in UTC time. The second column shows the output of TIMESTAMP_TRUNC using weeks that start on Monday. Because the timestamp_expression falls on a Sunday in UTC, TIMESTAMP_TRUNC truncates it to the preceding Monday. The third column shows the same function with the optional Time zone definition argument 'Pacific/Auckland'. Here, the function truncates the timestamp_expression using New Zealand Daylight Time, where it falls on a Monday.

SELECT
  timestamp_value AS timestamp_value,
  TIMESTAMP_TRUNC(timestamp_value, WEEK(MONDAY), "UTC") AS utc_truncated,
  TIMESTAMP_TRUNC(timestamp_value, WEEK(MONDAY), "Pacific/Auckland") AS nzdt_truncated
FROM (SELECT TIMESTAMP("2017-11-06 00:00:00+12") AS timestamp_value);

-- Display of results may differ, depending upon the environment and time zone where this query was executed.
/*-------------------------+-------------------------+-------------------------*
 | timestamp_value         | utc_truncated           | nzdt_truncated          |
 +-------------------------+-------------------------+-------------------------+
 | 2017-11-05 12:00:00 UTC | 2017-10-30 00:00:00 UTC | 2017-11-05 11:00:00 UTC |
 *-------------------------+-------------------------+-------------------------*/

In the following example, the original timestamp_expression is in the Gregorian calendar year 2015. However, TIMESTAMP_TRUNC with the ISOYEAR date part truncates the timestamp_expression to the beginning of the ISO year, not the Gregorian calendar year. The first Thursday of the 2015 calendar year was 2015-01-01, so the ISO year 2015 begins on the preceding Monday, 2014-12-29. Therefore the ISO year boundary preceding the timestamp_expression 2015-06-15 00:00:00+00 is 2014-12-29.

SELECT
  TIMESTAMP_TRUNC("2015-06-15 00:00:00+00", ISOYEAR) AS isoyear_boundary,
  EXTRACT(ISOYEAR FROM TIMESTAMP "2015-06-15 00:00:00+00") AS isoyear_number;

-- Display of results may differ, depending upon the environment and time zone where this query was executed.
/*-------------------------+----------------*
 | isoyear_boundary        | isoyear_number |
 +-------------------------+----------------+
 | 2014-12-29 00:00:00 UTC | 2015           |
 *-------------------------+----------------*/

UNIX_MICROS

UNIX_MICROS(timestamp_expression)

Description

Returns the number of microseconds since 1970-01-01 00:00:00 UTC.

Return Data Type

INT64

Examples

SELECT UNIX_MICROS(TIMESTAMP "2008-12-25 15:30:00+00") AS micros;

/*------------------*
 | micros           |
 +------------------+
 | 1230219000000000 |
 *------------------*/

UNIX_MILLIS

UNIX_MILLIS(timestamp_expression)

Description

Returns the number of milliseconds since 1970-01-01 00:00:00 UTC. Truncates higher levels of precision by rounding down to the beginning of the millisecond.

Return Data Type

INT64

Examples

SELECT UNIX_MILLIS(TIMESTAMP "2008-12-25 15:30:00+00") AS millis;

/*---------------*
 | millis        |
 +---------------+
 | 1230219000000 |
 *---------------*/

SELECT UNIX_MILLIS(TIMESTAMP "1970-01-01 00:00:00.0018+00") AS millis;

/*---------------*
 | millis        |
 +---------------+
 | 1             |
 *---------------*/

UNIX_SECONDS

UNIX_SECONDS(timestamp_expression)

Description

Returns the number of seconds since 1970-01-01 00:00:00 UTC. Truncates higher levels of precision by rounding down to the beginning of the second.

Return Data Type

INT64

Examples

SELECT UNIX_SECONDS(TIMESTAMP "2008-12-25 15:30:00+00") AS seconds;

/*------------*
 | seconds    |
 +------------+
 | 1230219000 |
 *------------*/

SELECT UNIX_SECONDS(TIMESTAMP "1970-01-01 00:00:01.8+00") AS seconds;

/*------------*
 | seconds    |
 +------------+
 | 1          |
 *------------*/

How time zones work with timestamp functions

A timestamp represents an absolute point in time, independent of any time zone. However, when a timestamp value is displayed, it's usually converted to a human-readable format consisting of a civil date and time (YYYY-MM-DD HH:MM:SS) and a time zone. This isn't the internal representation of the TIMESTAMP; it's only a human-understandable way to describe the point in time that the timestamp represents.

Some timestamp functions have a time zone argument. A time zone is needed to convert between civil time (YYYY-MM-DD HH:MM:SS) and the absolute time represented by a timestamp. A function like PARSE_TIMESTAMP takes an input string that represents a civil time and returns a timestamp that represents an absolute time. A time zone is needed for this conversion. A function like EXTRACT takes an input timestamp (absolute time) and converts it to civil time in order to extract a part of that civil time. This conversion requires a time zone. If no time zone is specified, the default time zone, UTC, is used.

Certain date and timestamp functions allow you to override the default time zone and specify a different one. You can specify a time zone by either supplying the time zone name (for example, America/Los_Angeles) or time zone offset from UTC (for example, -08).

To learn more about how time zones work with the TIMESTAMP type, see Time zones.

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