由于您的问题中没有样本数据集，我猜您得到的是相同的经理id、代理id。。。多次由于左连接得到正确的计数使用distinct

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

根据新版本，还可以将所有未聚合的列包含在group by中，因为大多数rdbms都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