Question

我能够在民意调查中得到总票数。但我需要得到选民没有投票的总数。例如，选民＃1仅投票给总统类别和参议员类别，选民＃2仅投票给副主席和参议员。最后，选民＃3没有投票，我仍然把选民投票＃3投票，并将其留空。所以结果应该是在特定类别中投票的数字选民。

PRESIDENT      : 2
VICE PRESIDENT : 2
SENATORS       : 1

在第1号选民没有投票支持vp的情况下，选民＃2没有投票支持pres，选民＃3则投了空票。

这是我的表格。

Polls
id | poll_title 
 1 | presidential election

Poll_categories
id | poll_id | category_name
 1 | 1       | President
 2 | 2       | Vice-President
 3 | 3       | Senator

Poll_items
id | poll_category_id | item_name
 1 | 1                | Obama
 2 | 1                | Bush
 3 | 1                | Clinton
 4 | 2                | Biden
 5 | 3                | Shelby
 6 | 3                | Murkowski

Poll_votes
id | voters_id | poll_item_id
 1 | 1         |  1
 2 | 1         |  5
 3 | 1         |  6
 4 | 2         |  4
 5 | 2         |  6
 6 | 3         |  NULL

到目前为止，这是我的查询，但我不知道接下来该做什么。我也无法显示elections_id 3，因为它是NULL

select c.id, c.category_name, v.voters_id from poll_category c
LEFT JOIN (select v.user_id, v.poll_item_id, i.poll_category_id as cat_id, i.item_name 
           from poll_votes v 
           LEFT JOIN poll_items i on i.id = v.poll_item_id) v
    ON v.cat_id = c.id
WHERE c.poll_id = 1

Answer 1

您可以使用以下查询：

SELECT pc.id, COUNT(*)
FROM Poll_categories AS pc
CROSS JOIN (
   SELECT DISTINCT voters_id
   FROM Poll_votes) AS voters
LEFT JOIN (
  SELECT voters_id, poll_category_id
  FROM Poll_votes AS pv
  LEFT JOIN Poll_items AS pi ON pv.poll_item_id = pi.id
) AS voters_cat 
  ON pc.id = voters_cat.poll_category_id AND voters.voters_id = voters_cat.voters_id
WHERE voters_cat.poll_category_id IS NULL
GROUP BY id

Demo here

如何获得对特定民意投票不投票的选民的数量

1 个答案: