MySQL - 与主表连接两次表格

Question

我不确定这是否可以完成。但我只是想和这里的专家核对一下。

我的情况是： 我有基本上存储一个广告活动时，有一个人跟在竞选期间被选中的用户与广告活动编号（tbl_campagin_user一起存储的表称为tbl_campaign_user许多关系的表tbl_campaign。 cu_campaign_id = tbl_campaign.campaign_id）。

第二张表（tbl_campaign_user）的状态字段为0/1表示未发送/发送。我想写一个单独的sql查询来读取活动数据以及发送和未发送活动用户的数量（这就是为什么我要在第二个表上连接两次）。 我在下面尝试了这一点，但我得到了与发送和未发送相同数量的计数。

SELECT `tbl_campaign`.*, 
COUNT(sent.cu_id) as numsent, 
COUNT(unsent.cu_id) as num_unsent FROM (`tbl_campaign`) 

LEFT JOIN tbl_campaign_user as sent on (sent.cu_campaign_id = tbl_campaign.campaign_id and sent.cu_status='1') 

LEFT JOIN tbl_campaign_user as unsent on (unsent.cu_campaign_id = tbl_campaign.campaign_id and unsent.cu_status='0') 


WHERE `tbl_campaign`.`campaign_id` = '19' 

---

我试着调试通过打破查询分成两个部分： =>

SELECT `tbl_campaign`.*, 

COUNT(unsent.cu_id) as num_unsent FROM (`tbl_campaign`) 

Left join tbl_campaign_user as unsent on (unsent.cu_campaign_id = tbl_campaign.campaign_id and unsent.cu_status='0') 

WHERE `tbl_campaign`.`campaign_id` = '19' 

---

上述作品正是被通缉。所以做下一个：我不知道我已经做错了，而合并两个

=>

SELECT `tbl_campaign`.*, 
COUNT(sent.cu_id) as numsent FROM (`tbl_campaign`) 

Left join tbl_campaign_user as sent on (sent.cu_campaign_id = tbl_campaign.campaign_id and sent.cu_status='1') 

WHERE `tbl_campaign`.`campaign_id` = '19' 

---

。我知道我对加入的了解不多，所以可能是一个概念错误？请任何人都可以帮我吗？

Thx提前！

Answer 1

您只需要加入tbl_campaign_user一次，并且 count（总和，无论）cu_status是零次/一次多少次。

SELECT `tbl_campaign`.id, 
count(u.id) as num_all_campaign_users 
sum(u.cu_status) as num_sentcampaign_users, 
count(u.id) - sum(u.cu_status) as num_unsent_campaign_users 
FROM `tbl_campaign` c 
LEFT JOIN tbl_campaign_user as u on (u.cu_campaign_id = c.campaign_id) 
WHERE `tbl_campaign`.`campaign_id` = '19' 
group by `tbl_campaign`.id 

注意，这是有点伪代码，你可能要阐述 总和/ BY子句select子句和组数为好。