小编kha*_*rul的帖子

我正在使用count并group by获得每天注册的订阅者数量:

  SELECT created_at, COUNT(email)  
    FROM subscriptions 
GROUP BY created at;

结果:

created_at  count
-----------------
04-04-2011  100
05-04-2011   50
06-04-2011   50
07-04-2011  300

我想每天获得累计订阅者总数.我怎么得到这个？

created_at  count
-----------------
04-04-2011  100
05-04-2011  150
06-04-2011  200
07-04-2011  500

我想检索柏林时区记录的每日注册数量,但默认情况下我的数据库使用时区'-08'.如何select在指定时区时进行声明？

我有两组结果:

SELECT name, count(appearance) as countA from table where results = '1'
SELECT name, count(appearance) as countB from table where results = '2'

我希望将它们并排组合,如下所示:

+---------+---------+---------+
| col_1   | countA  | countB  |
+---------+---------+---------+
| John    |    3    |    1    |
| Mary    |    1    |    2    |
| Gary    |    2    |   NULL  |
| Sean    |    4    |   NULL  |
| Mike    |  NULL   |    6    |
+---------+---------+---------+

我怎么做？

我正在使用count并group by了解每天有多少订阅者购买:

select count(s.email) 
from subscriptions s, orders o 
where o.subcription_id=s.id 
group by s.created_at

结果:

created_at  count
------------------
04-04-2011  1
06-04-2011  2
07-04-2011  1
10-04-2011  5
11-04-2011  9

但是我仍然希望空行返回为'0'.我该怎么做呢？请注意,我必须使用这两个表.

created_at  count
------------------
04-04-2011  1
05-04-2011  0
06-04-2011  2
07-04-2011  1
08-04-2011  0
09-04-2011  0
10-04-2011  5
11-04-2011  9

要调用此部分视图:

<% form_for(:subscription, :url => city_subscriptions_path(@city)) do |form| %>
  <%= form.hidden_field :city_id, :value => @city.id %>
  <%= form.text_field :email, :size => 30 %>
  <%= form.submit "Email Me" %>
<% end %>

由于我在不同的地方使用这个局部视图,如何更改调用者以便它将为form_for助手传递哈希？所以当调用帮助器时会是这样的:

<% form_for(:subscription, :url => city_subscriptions_path(@city), :html => {:id => 'main_input' }) do |form| %>
  <%= form.hidden_field :city_id, :value => @city.id %>
  <%= form.text_field :email, :size => 30 %>
  <%= form.submit "Email Me" %>
<% end %>

我有一个名为userswith a column 的表activated_at,我想通过检查列是否为null来计算已激活的用户数.然后像这样并排显示它们:

+----------+-----------+---------------+-------+
| Malaysia | Activated | Not Activated | Total |
+----------+-----------+---------------+-------+
| Malaysia |      5487 |           303 |  5790 | 
+----------+-----------+---------------+-------+

这是我的SQL:

select "Malaysia",
    (select count(*) from users where activated_at is not null and locale='en' and  date_format(created_at,'%m')=date_format(now(),'%m')) as "Activated",
    (select count(*) from users where activated_at is null and locale='en' and  date_format(created_at,'%m')=date_format(now(),'%m')) as "Not Activated",
    count(*) as "Total"
    from users 
    where locale="en"
    and  date_format(created_at,'%m')=date_format(now(),'%m');

在我的代码中,我必须指定所有where语句三次,这显然是多余的.我怎么能重构这个？

此致,MK.