MySQL左外部联接未提供正确的值

Question

我有以下表格和关系

这里是样本数据-

我尝试了以下查询-

 SELECT project.*, SUM(schedule.amount) as sch_total, SUM(expense.amount) as expense_total, SUM(bill.amount) as bill_total from project 
LEFT OUTER JOIN schedule on project.project_id = schedule.project_id 
LEFT OUTER JOIN site on project.project_id = site.project_id 
LEFT OUTER JOIN expense on site.site_id = expense.site_id 
LEFT OUTER JOIN bill on site.site_id = bill.site_id 
GROUP BY project.project_id

这是查询结果-

但是“ bill_total”应该是200，而不是400。我在查询中错过了什么？

Answer 1

您的费用表具有相同ID的多行。该表必须首先聚合，然后在连接中使用-