聚合函数或GROUP BY子句

Question

我用下面的查询：

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

，但我得到了以下错误：

Msg 8120, Level 16, State 1, Line 1 Column 'Patients.LastName' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

Answer 1

你需要一个GROUP BY添加到您的查询：

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

SQL Server要求您的SELECT列表中的任何列不在聚合函数b中e包含在GROUP BY中。由于您在汇总数据时试图返回Patients.LastName，因此您必须在该组中包含该列。