连接表，计数和日期

Question

我想加入两个 table 并根据日期从一个中检索计数。

我有一个tableaccess_points:

access_points_id, access_points_name

和另一个 table access_points_launched:

access_points_launched_id, access_points_name, launched_date

我想 return 所有 access_points 计算当前日期在 access_points_launched 中有多少条目：

Access Point, Launched Count, Date
WIFI_point, 2, 05/01/2015
FREE_INTERNET, 0, 05/01/2015
SPRINT_INTERNET, 5, 05/01/2015

我不希望计数包括任何其他日期。

有什么想法吗？

Answer 1

您可以在子查询中获得聚合计数，并且可以执行 left join 和 access_points table 以获得所需的结果。

select a.access_points_name, aggr.totalCount , curdate()
from access_points a
left join ( select access_points_name, count(*) as totalCount
            from access_points_launched
            where date(launched_date) = curdate() 
            group by access_points_name
          ) aggr
on aggr.access_points_name =  a.access_points_name

连接表，计数和日期

Joining tables, with counts, and dates

mysql