date_trunc

Truncates a DateTime value to the specified window/precision. Given an input timestamp this function returns the start time of the time window that contains the input timestamp.

date_trunc(window, timestamp)

The window parameter must be a string and must be equal to or end with one of the time units below. Optionally, you can prefix the time unit with an integral number to make the window a multiple of the unit.

The valid time units are:

ms/msec/millisecond/milliseconds
s/sec/second/seconds
min/minute/minutes
h/hour/hours
d/day/days
w/week/weeks
month/months
y/year/years

Examples:

SELECT date_trunc('hour', FROM_TIMESTAMP(1486553343));
Result: 2017-02-08 11:00:00

SELECT date_trunc('10min', FROM_TIMESTAMP(1486553343));
Result: 2001-02-16 11:20:00