聚合函数或GROUP BY子句

Question

我使用了以下查询:

select Patients.LastName, 
  avg (PatientVisits.Pulse)as pulse,
  avg (patientvisits.depressionlevel)as depressionLevel  
from Patients 
left join PatientVisits 
   on Patients.PatientKey=PatientVisits.PatientKey

但是我收到以下错误:

消息8120,级别16,状态1,行1列"Patients.LastName"在选择列表中无效,因为它不包含在聚合函数或GROUP BY子句中.

Answer 1

您需要GROUP BY在查询中添加一个:

select Patients.LastName, 
   avg (PatientVisits.Pulse)as pulse,
   avg (patientvisits.depressionlevel)as depressionLevel  
from Patients 
left join PatientVisits 
  on Patients.PatientKey=PatientVisits.PatientKey 
GROUP BY Patients.LastName

SQL Server要求SELECT列表中不在聚合函数中的任何列都包含在a中GROUP BY.由于您在Patients.LastName聚合数据时尝试返回,因此必须在组中包含该列.