BigQuery - 星期一 = 1 的星期几

Question

Is there a standard way to return "day of week number" (1-7) in ISO standard (Monday = 1) from a date in BigQuery using built in functions?

EXTRACT(DAYOFWEEK, <date>) returns a number using US format ie Sunday = 1, which doesn't work for my purpose.

I can create a custom function to calculate the ISO day of week number but I'm not sure whether I'm missing something built in that I can use instead.

Answer 1

您可以使用模运算转换为 ISO 标准（星期一 = 1）：

MOD(EXTRACT(DAYOFWEEK FROM <date>) + 5, 7) + 1

Answer 2

Below is example of such function - just one of many options you can come with

#standardSQL
CREATE TEMP FUNCTION ISODAYOFWEEK(day DATE) AS ((
  SELECT IF(weekday = 0, 7, weekday) 
  FROM UNNEST([EXTRACT(DAYOFWEEK FROM day) - 1]) weekday 
));

Answer 3

I end up defining a custom function for better readability

CREATE TEMP FUNCTION timestampToWeekday(dt timestamp) AS (CASE WHEN EXTRACT(DAYOFWEEK FROM dt)-1 = 0 THEN 7 ELSE EXTRACT(DAYOFWEEK FROM dt)-1 END);

And now I can use this function to convert any timestamp to a weekday.