不是唯一的表/别名（42000）

Question

我得到的错误ERROR 1066（42000）：不是唯一的表/别名： 'STUDENT_TBL'

select STUDENT,DATE,MARK from Assessments inner join STUDENT_TBL onAssessments,ID_STUDENT=STUDENT_TBL,STD_ID inner joinVisit_log,ID_STUDENT=STUDENT_TBL,STD_ID where STUDENT_TBL,STD_IDIN (select ID_STUDENT FROM Assessments group by ID_STUDENT having avg(MARK)>3.7);

如何解决呢？

Answer 1

您应该使用的'.'代替','访问Table_Name.column_name。

select STUDENT,DATE,MARK 
from Assessments AS Assessments 
inner join STUDENT_TBL AS STUDENT_TBL on Assessments.ID_STUDENT=STUDENT_TBL.STD_ID 
inner join Visit_log AS Visit_log on Visit_log.ID_STUDENT=STUDENT_TBL.STD_ID 
where STUDENT_TBL.STD_ID IN (select ID_STUDENT FROM Assessments 
          group by ID_STUDENT having avg(MARK)>3.7 

还可以使用别名等Assessments.ID_STUDENT而在选择子句选择列，如果这些存在于一个以上的表

Answer 2

如果您使用的模式和表名，你必须用单独的点像这样

select STUDENT, Assessments .`DATE`,MARK from Assessments 
inner join STUDENT_TBL on Assessments.ID_STUDENT=STUDENT_TBL.STD_ID 
inner join Visit_log.ID_STUDENT=STUDENT_TBL.STD_ID 
where STUDENT_TBL.STD_ID IN (select ID_STUDENT FROM Assessments group by ID_STUDENT having avg(MARK)>3.7);