加入这些表时为什么会出现错误？

Question

I am trying to joining these two tables but I am getting an error code?

SELECT LoanNumber, LetterDescription, LetterID, LetterDate, LetterProcessingDate
FROM PortfolioData.dbo.LetterData L
WHERE LetterID IN ('DF013', 'LM002')
LEFT JOIN MainServicing
ON Letterdata.LoanNumber = MainServicing.Loannumber

SELECT Loannumber,Lo_TypeDesc,Inv_ID,Investor_Desc,NPDD,UPB,cast(Date_Archived as date) as Date_Archived
FROM PortfolioData.dbo.MainServicing
WHERE Lo_TypeDesc IN ('USDA RHS') OR Investor_Desc IN ('FNMA','FHLMC')
AND (DATEDIFF(day,LetterDate,Date_Archived)<30)
 

Answer 1

SELECT L.LoanNumber, L.LetterDescription, L.LetterID, L.LetterDate, LetterProcessingDate
FROM PortfolioData.dbo.LetterData L  <---- Alias Here
WHERE LetterID IN ('DF013', 'LM002')
LEFT JOIN MainServicing M <---- Alias Here (Add it)
ON L.LoanNumber = M.Loannumber

You have an alias in the from statement, try using the alias L on the LoanNumber and your other fields specific to your select statements. I would also consider adding M or some alias. Note you have LoanNumber which looks like it resides in both tables so you would need to qualify that so the select knows which table to go to.