SQL Resources/BigQuery/DATETIME_DIFF

DATETIME_DIFF

Definition

The DATETIME_DIFF function in BigQuery allows you to find the difference between 2 DATETIMEs in the specified date_part interval.

Syntax

DATETIME_DIFF(datetime_expression_a, datetime_expression_b, date_part)

Where date_part can be any of the following:

  • MICROSECOND
  • MILLISECOND
  • SECOND
  • MINUTE
  • DAY
  • WEEK : Begins on Sunday
  • WEEK(<WEEKDAY>): Begins on <WEEKDAY> where WEEKDAY can be SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, and SATURDAY.
  • ISOWEEK: Uses ISO 8601 week boundaries. ISO weeks begin on Monday.
  • MONTH
  • QUARTER
  • YEAR
  • ISOYEAR: Uses the ISO 8601 week-numbering year boundary. The ISO year boundary is the Monday of the first week whose Thursday belongs to the corresponding Gregorian calendar year.

Returns: INT64

SELECT
  DATETIME_DIFF(CAST('2021-01-01 14:01:05' AS DATETIME), CAST('2021-01-01 12:22:23' AS DATETIME), MINUTE) AS minutes_difference,
  DATETIME_DIFF(CAST('2021-01-01 04:44:33' AS DATETIME), CAST('2020-06-22' AS DATETIME), QUARTER) AS quarter_difference
minutes_difference
99
quarter_difference
3

Practical Info

  • If the first DATETIME is earlier than the second one then the output will be negative
  • Throws an error if the computation overflows the result type, such as if the difference in microseconds between the two DATETIME objects would overflow an INT64 value.

Common Questions

How to filter for the last n days?

A common SQL query WHERE clause is to just pull the data for the last n days. In this case, we can make use of DATETIME_DIFF and CURRENT_DATETIME:

SELECT
  date,
  DATETIME_DIFF(CURRENT_DATETIME(), date, DAY) AS days_since
FROM
  (
    SELECT
      CAST('2021-01-22' AS DATETIME) AS date
    UNION ALL
(    SELECT
      CAST('2020-01-25' AS DATETIME) AS date)
    UNION ALL
(    SELECT
      CAST('2021-01-26' AS DATETIME) AS date)
  ) AS table_3
WHERE
  (DATETIME_DIFF(CURRENT_DATETIME(), date, DAY) <= 30)
date
2021-01-22T00:00:00
2021-01-26T00:00:00
days_since
21
17

Troubleshooting Common Errors

Argument 2 of DATETIME_DIFF has incorrect type: expected datetime found date.

This one is all too common. If you're using DATETIME_DIFF, you'll need to make sure both of your datetimes are indeed DATETIME data types, and not DATEs or TIMESTAMPs. It's usually easy enough to add a CAST(datetime_col as DATETIME) to your function:

DATETIME_DIFF(CAST('2020-01-01' as DATETIME),'2021-01-05 03:04:00', DAY) days_diff

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