mysql一天一天地选择日期

Question

I have table shown below :

                      login
          date                     user    
       2016-11-23                   1
       2016-11-23                   2
       2016-11-23                   3
       2016-11-25                   2
       2016-11-25                   5
       2016-11-27                   1

from above table what I want to get is like this:

      date                   count(*)
   2016-11-21                   0
   2016-11-22                   0    
   2016-11-23                   3
   2016-11-24                   0
   2016-11-25                   2
   2016-11-26                   0
   2016-11-27                   1

But, because there are only dates 2016-11-23 and 2016-11-25 and 2016-11-27 , when I query like this :

select date, count(*)
from login
where date between (current_date()-interval 7 day) and current_date()
group by date
order by date asc

It can't get result like what I really want to get. Is that result possible from my login table?

Answer 1

One way is to generate all days before JOIN

select GenDate, count(Date)
from login
right join
(select a.GenDate 
from (
    select curdate() - INTERVAL (a.a + (10 * b.a) + (100 * c.a)) DAY as GenDate
    from (select 0 as a union all select 1 union all select 2 union all select 3 union all select 4 union all select 5 union all select 6 union all select 7 union all select 8 union all select 9) as a
    cross join (select 0 as a union all select 1 union all select 2 union all select 3 union all select 4 union all select 5 union all select 6 union all select 7 union all select 8 union all select 9) as b
    cross join (select 0 as a union all select 1 union all select 2 union all select 3 union all select 4 union all select 5 union all select 6 union all select 7 union all select 8 union all select 9) as c
) a
where a.GenDate between (current_date()-interval 7 day) and current_date())x
ON x.GenDate=login.Date
group by GenDate
order by GenDate asc

Answer 2

Use a derived table with the wanted dates :

SELECT t.date, count(s.date)
FROM (SELECT '2016-11-21' as `date` UNION ALL
      SELECT '2016-11-22' as `date` UNION ALL
       ...) t
LEFT JOIN login s
 ON(t.date = s.date)
WHERE
    t.date between (current_date()-interval 7 day) and current_date()
GROUP BY t.date
ORDER BY t.date

Answer 3

This is a very well known problem in programming. There are several solutions.

1. Go over the result with PHP, and fill the missing days in the resulting array.

2. AS sagi proposed, create a separate table that contains all the dates in the range of days your application works with, then you can JOIN that table with your query. One of the issues is that from time to time you have to add more days to this table, if you suddenly have missing days in future or in past.