Group by date (day,week,month,year) from unixtimestamp

SQL++
6

has solution

SELECT SUM(TO_NUMBER(o.total_gross_amount)) AS OrderGrossSales, COUNT(1) AS OrderCount, wdt AS week
FROM order AS o
LET dt = MILLIS_TO_STR(o.received_date_time,"1111-11-11"),
    wdt = DATE_ADD_STR(dt, {"Sunday":0,"Monday":-1,"Tuesday":-2,"Wednesday":-3,"Thursday":-4,"Friday":-5,"Saturday":-6}.[WEEKDAY_STR(dt)],"day")
WHERE dt BETWEEN "2021-01-01" AND "2021-03-08"
GROUP BY wdt
ORDER BY wdt;

test start of week

SELECT wdt
LET dt = MILLIS_TO_STR(MILLIS("2021-01-05"),"1111-11-11"),
    wdt = DATE_ADD_STR(dt, {"Sunday":0,"Monday":-1,"Tuesday":-2,"Wednesday":-3,"Thursday":-4,"Friday":-5,"Saturday":-6}.[WEEKDAY_STR(dt)],"day");