如果没有结果，mysql选择日期的默认值

Question

我有一个按天分组的付款表

select
 day(created),
 sum(payments.amount) 
from payments
group by day(created)

输出

day | amount
1   | 432
2   | 4567
5   | 345
6   | 2345
7   | 97

这很好，但我想在没有付款的日子里添加一些0。

预期输出:

day | amount
1   | 432
2   | 4567
3   | 0
4   | 0
5   | 345
6   | 2345
7   | 97

Answer 1

由于您在付款表中没有所有日期，您可以执行以下操作:

select
    d,
    ifnull(sum(p.amount),0) sum_amount
from (
         select 1 as d
         union all 
         select 2
         union all 
         select 3
         union all 
         select 4
         union all 
         select 5
         union all 
         select 6
         union all 
         select 7
    ) d
    left join payments p 
    on day(p.created) = d.d
group by d
order by d

示例:http://sqlfiddle.com/#!9/cb09d1/2