SQL: select 客户营业额最大的年份和月份怎么办？

Question

I need to List top 10 customers by average monthly transactions amount turnover, in additional column indicating the year and month with highest monthly turnover of the customer.

I made the first part - list top 10 customers by average monthly transactions amount turnover.

Select column1, AVG(Case when when column1="x" then column2
                      when column1="y" then column2
                      when column1="z" then column2
                      when column1="q" then column2 End)/12 [AVG]
from table1
Group by column1
Order by AVG DESC;

How to make the second part of the task - in additional column indicating the year and month with highest monthly turnover of the customer?

Answer 1

This sounds like aggregation and window functions. Date functions are notoriously database-dependent, but the idea is:

select ymc.*
from (select year(r_date) as yyyy, month(r_date) as mm, c_id, sum(amount) as amount,
             row_number() over (partition by c_id order by sum(amount) desc) as seqnum
      from t
      group by year(r_date), month(r_date), c_id
     ) ymc
where seqnum = 1;

Not all databases support year() and month() but all have similar functionality. So you may need to modify for what your database uses.

Answer 2

Use below query, below query in for Oracle, tag your database so that can provide appropriate query.

select c_id, to_char(r_date, 'MM'), to_char(r_date, 'YYYY'), max(amount)
group by c_id, to_char(r_date, 'MM'), to_char(r_date, 'YYYY');