Oracle按日期，月份和年份分组

Question

I have the below query to show me the count for each country group by single days such as 20160101.

How can I modify the below query so it can group by date, month and year?

Please note currently working on an Oracle database.

Many Thanks in advance.

Select count(1), country_of_sale, substr(datefield,1,8) AS datefield1
from table 
where country_of_sale IN (‘USA’,’EUROPE’,’ASIA’)
group by country_of_sale, substr(datefield,1,8)
order by substr(datefield,1,8)

Answer 1

If datefield is a string, then just use substr() . For year and month:

Select count(1), country_of_sale, substr(datefield, 1, 6) AS yyyymm
from table 
where country_of_sale IN ('USA', 'EUROPE', 'ASIA')
group by country_of_sale, substr(datefield, 1, 6)
order by substr(datefield, 1, 6);

If datefield is a date, then use to_char() :

Select count(1), country_of_sale, to_char(datefield, 'YYYY-MM') AS yyyymm
from table 
where country_of_sale IN ('USA', 'EUROPE', 'ASIA')
group by country_of_sale, to_char(datefield, 'YYYY-MM')
order by to_char(datefield, 'YYYY-MM');

Answer 2

It would be smart to use dedicated functionality. Playing with strings will work, but can be slower and it also assumes things about your date/time formatting etc.

Oracle has a TRUNC function, which "rounds down" a date to a day, month, etc.