MySQL 查询返回错误的 COUNT 值

Question

在这里我分享了我的疑问。所有总计值都会给出错误的结果，因为非常大的数值不是所需的 COUNT 值。我的查询有什么问题？

           SELECT bd.business_id,
                  bd.business_name,
                  bd.business_address,
                  bd.created_at,
                  bd.updated_at AS extent_expiry_date,
                  bd.manager_id as user_id,
                  COUNT(m.manager_id) AS total_managers,
                  COUNT(a.agent_id) AS total_agents,
                  COUNT(c.customer_id) AS total_customers,
                  COUNT(t.task_id) AS total_tasks,
                  COUNT(t.order_id) AS total_orders
            FROM business_details bd
            LEFT JOIN managers m ON m.business_id = bd.business_id
            LEFT JOIN agents a ON a.business_id = bd.business_id
            LEFT JOIN customers c ON c.business_id = bd.business_id
            LEFT JOIN tasks t ON t.business_id = bd.business_id
            GROUP BY bd.business_id

Answer 1

由于您的问题中没有示例数据集，我的猜测是您多次获得相同的 manager_id、agent_id...，因为左连接使用不同的值来获取正确的计数

SELECT bd.business_id,
      bd.business_name,
      bd.business_address,
      bd.created_at,
      bd.updated_at AS extent_expiry_date,
      bd.manager_id as user_id,
      COUNT(distinct m.manager_id) AS total_managers,
      COUNT(distinct a.agent_id) AS total_agents,
      COUNT(distinct c.customer_id) AS total_customers,
      COUNT(distinct t.task_id) AS total_tasks,
      COUNT(distinct t.order_id) AS total_orders
FROM business_details bd
LEFT JOIN managers m ON m.business_id = bd.business_id
LEFT JOIN agents a ON a.business_id = bd.business_id
LEFT JOIN customers c ON c.business_id = bd.business_id
LEFT JOIN tasks t ON t.business_id = bd.business_id
GROUP BY bd.business_id

还包括分组依据中的所有非聚合列，因为根据新版本，大多数 RDBMS 拒绝这些类型的查询

GROUP BY 
bd.business_id,
bd.business_name,
bd.business_address,
bd.created_at,
bd.updated_at,
bd.manager_id