generate empty rows even if empty between 2 dates

Question

I have this simple query that fetches all completed orders between 2 dates(about 6 months at a time):

select IFNULL(sum(o.amount), 0) as amount, o.completed_         


        

Answer 1

Here is what you need:

1] create an auxiliary table

 create table db.myDates(
   completed_at date not null
 )

2] fill the table with the months in range, for example:

 insert into db.myDates values('2011-10-01'),
 ('2011-11-01'),
 ('2011-12-01'),
 ('2012-01-01'),
 ('2012-02-01'),
 ('2012-03-01');

3] then select:

 select a.completed_at, sum(b.amount)
 from myDates a
 left join orders b 
   on extract(year_month from a.completed_at)=extract(year_month from b.completed_at)
     and date(b.completed_at) between '2012-01-05' and '2012-06-05'
 group by year(b.completed_at)), month(dateCompleted)
 order by a.completed_at;

the result looks like this (dates mine)

2012-01-01  27
2012-02-01  NULL
2012-03-01  47
2012-04-01  13
2012-05-01  12
2012-06-01  15

Answer 2

This query is complicated due to a number of factors.

The easiest solution might be to add a 0 amount on the first of each month.

Answer 3

Try with coalesce function which will return '0' if the sum(orders.amount) is null for a specific month:

select COALESCE(sum(o.amount), 0) as amount, o.completed_at 
from orders o 
where date(o.completed_at) between '2011/10/01' and '2012/03/06' 
group by year(o.completed_at), month(o.completed_at) order by o.completed_at