INTERVAL function
Returns the time interval between two DATE, DATETIME, or DATETIME-TZ values as an INT64 value.
Syntax
INTERVAL (datetime1, datetime2, interval-unit)
datetime1
An expression whose value is a DATE, DATETIME, or DATETIME-TZ.
datetime2
An expression whose value is a DATE, DATETIME, or DATETIME-TZ.
interval-unit
A character constant, or a character expression that evaluates to one of the following time units: ‘years’, ‘months’, ‘weeks’, ‘days’, 'hours’, ‘minutes’, ‘seconds’ or ‘milliseconds’. These values are case insensitive and might be singular.
Notes
This function returns a signed integer value (positive or negative). For example, if datetime1 is less than datetime2, the INTERVAL function returns a negative value.
If datetime1 or datetime2 is a DATE or DATETIME, the time value defaults to midnight and the time zone value defaults to the session's time zone, respectively.