如何在sql中使用groupby，distinct

Question

This is the table data

表名是voyagemaster。如何选择不同的船只和一艘船只有很多航程号，因此我添加了航行 选择voyagenumber为max（voyagedate）。 根据船只选择max（voyagedate）和voyagenumber。 怎么解决..

select distinct(Vessel), VoyageID, VoyageNumber, max(VoyageDate) as vdate, VIA,
       ROTNo, CutOffDate, CutOffTime, ETA, ETD
from VoyageMaster
group by Vessel 

先谢谢

Answer 1

试试这个：

SELECT A.Vessel,V1.VoyageID,V1.VoyageNumber,A.VoyageDate 
FROM VoyageMaster V1 
JOIN ( SELECT Vessel,MAX(VoyageDate) VoyageDate  
       FROM VoyageMaster 
       GROUP BY Vessel ) A 
  ON A.Vessel = V1.Vessel 
  AND V1.VoyageDate = A.VoyageDate

Answer 2

试试这个：

SELECT * from VoyageMaster
where VoyageDate in (select max(VoyageDate)from VoyageMaster group by vessel) 

或仅包含您想要的列：

SELECT Vessel,VoyageID,VoyageNumber,VoyageDate,VIA,ROTNo,CutOffDate,CutOffTime,ETA,ETD
from VoyageMaster
where VoyageDate in (select max(VoyageDate)from VoyageMaster group by vessel)