mysql - 输出两个关联表的总计的查询未正确返回总计，为什么？

Question

您好，我有以下数据库架构，3 个表:

connected_accounts (fields: id, user_id, account_name)
contacts (fields: id, user_id, connected_account_id, type)
user_recommendations (fields: id, user_id, contact_id)

我正在尝试输出一个查询，该查询显示数据库中每个 connect_account 记录、关联的联系人和 user_recommendations 的总数。这是我到目前为止所拥有的:

SELECT 
    ca.id, 
    ca.user_id, 
    ca.account_name,
    COUNT(c.id) AS Total
FROM connected_accounts ca
LEFT JOIN contacts c
     ON ca.id = c.connected_account_id
       AND c.contact_type = 'email'
WHERE ca.resource_type = 'calendar.readonly'
ORDER BY ca.id DESC
LIMIT 8

这无法正常工作...所需的输出如下所示:

结果

id | user_id | account_name | Total Contacts | Total User Recommendations

我尚未加入 UserRecommendations，因为我的联系人加入功能未按预期工作。

我在查询中做错了什么？谢谢

更新:

SELECT 
    ca.id, 
    ca.user_id, 
    ca.account_name,
    COUNT(c.id) AS 'Total Contacts',
    COUNT(pr.id) AS 'Total User Rec.'
FROM connected_accounts ca

LEFT JOIN contacts c
     ON ca.id = c.connected_account_id
       AND c.contact_type = 'email'

LEFT JOIN user_recommendations pr
     ON ca.id = pr.connected_account_id

WHERE ca.resource_type = 'calendar.readonly'
GROUP BY ca.id, ca.user_id, ca.account_name
ORDER BY ca.id DESC
LIMIT 8

上面已更新.. 上述更新后的查询为 Total Contacts 和 Total User Rec 返回相同的 # — 该数字对于两者来说是相同的联系人总数的正确数字。用户记录总数未返回...为什么？

Answer 1

您错过了GROUP BY。尝试这个。希望能帮助到你。 另外，LEFT JOIN 将拥有 connected_accounts 表中的所有记录，这是您想要的吗？

SELECT 
    ca.id, 
    ca.user_id, 
    ca.account_name,
    COUNT(c.id) AS Total
FROM connected_accounts ca
LEFT JOIN contacts c
     ON ca.id = c.connected_account_id
       AND c.contact_type = 'email'
WHERE ca.resource_type = 'calendar.readonly'
GROUP BY ca.id, ca.user_id, ca.account_name
ORDER BY ca.id DESC
LIMIT 8