MySQL加入这里是最好的选择吗？ 活动： 服务：

查询结果应显示：

campaigns_id    campaigns_name          cap    count
1               Campaign1               2      2
2               Campaign2               1      1
3               Campaign3               1      0

我正在使用此查询：

   SELECT served.id_campaign, 
          campaigns.name, 
          campaigns.cap, 
          COUNT( served.id ) AS count
     FROM campaigns
LEFT JOIN served ON campaigns.id = served.id_campaign
    WHERE served.ip =  '127.0.0.1' 
 GROUP BY served.id_campaign

我的查询显示这些结果不正确，没有显示活动id。3：

campaigns_id    campaigns_name          cap    count
1               Campaign1               2      2
2               Campaign2               1      1

---

如果我想包含WHERE语句未选择的值，我认为我的做法是错误的，因为服务中没有与活动的WHERE语句匹配的记录。id='3'

LEFT JOIN表示从左侧表中获取所有记录，并从右侧表中获取匹配的记录。因此，从id=3开始，served.ip将为NULL。 因此，更改where条件以使其

WHERE serverd.ip = '127.0.0.1' or serverd.ip IS NULL

---

将where子句更改为

WHERE served.ip =  '127.0.0.1' OR served.ip IS NULL

新编辑：

   SELECT campaigns.id as id_campaign, 
          campaigns.name, 
          campaigns.cap, 
          COUNT( served.id ) AS count
     FROM campaigns
LEFT JOIN served ON campaigns.id = served.id_campaign
      AND served.ip =  '127.0.0.1' 
 GROUP BY campaigns.id

旧职位：

我提出了这个查询，它生成您想要的结果：

(SELECT served.id_campaign, 
          campaigns.name, 
          campaigns.cap, 
          COUNT( served.id ) AS count
     FROM campaigns
LEFT JOIN served ON campaigns.id = served.id_campaign
    WHERE served.ip =  '127.0.0.1' 
 GROUP BY served.id_campaign)

UNION

(SELECT id, name, cap, 0 as count 
FROM campaigns 
WHERE id <> ALL 
     (
      SELECT campaigns.id 
      FROM campaigns, served 
      WHERE campaigns.id = served.id_campaign AND served.ip = "127.0.0.1"
     )
)

---

正如您可以从输出中看到的，我希望下面的输出显示查询结果，我希望包含id 3的结果。LEFT JOIN和JOIN在这里返回相同的输出。哦，对不起，我刚才跳过了它。请尝试此served.ip='127.0.0.1'或served.ip为空。它工作的原因是resultset中的served.ip将为空或null。希望有帮助。我不能这样做，因为我需要从服务中选择与特定IP匹配的记录。这样做本质上就是做一个WHERE 1=1语句。不，不是。基本上是说，如果服务器IP为“127.0.0.1”或未设置服务器IP，则只显示记录。它将排除所有其他IP。我明白你的意思。我误解了答案。这将不起作用，因为始终存在served.ip的值，并且由于served中没有关联行，因此缺少活动中缺少的行。这起作用，但加载查询花费了26秒。有超过300000行。也许有一种方法可以执行查询，而不必通过服务查询两次。这是安德烈M.的更正查询。我认为应该可以，它只查询了一次服务的表。享受我认为在选择列表中将served.id_活动替换为campaiments.id是个好主意。您的新查询现在似乎只需要一个更正：GROUPBY子句可能应该是GROUPBY MAVICES.id。更新：我冒昧地编辑了你的文章。如果您不同意，请随时回滚更改。

   SELECT campaigns.id as id_campaign, 
          campaigns.name, 
          campaigns.cap, 
          COUNT( served.id ) AS count
     FROM campaigns
LEFT JOIN served ON campaigns.id = served.id_campaign
      AND served.ip =  '127.0.0.1' 
 GROUP BY campaigns.id

(SELECT served.id_campaign, 
          campaigns.name, 
          campaigns.cap, 
          COUNT( served.id ) AS count
     FROM campaigns
LEFT JOIN served ON campaigns.id = served.id_campaign
    WHERE served.ip =  '127.0.0.1' 
 GROUP BY served.id_campaign)

UNION

(SELECT id, name, cap, 0 as count 
FROM campaigns 
WHERE id <> ALL 
     (
      SELECT campaigns.id 
      FROM campaigns, served 
      WHERE campaigns.id = served.id_campaign AND served.ip = "127.0.0.1"
     )
)