SQL Server中的案例声明

Question

I am learning SQL case statements and have the following stored procedure .

Select PT.[ID] 'TransactionID', PT.BatchNumber, PT.SequenceNumber, PT.TransactionDate,  
PT.TerminalID, PT.TotalAmount, PT.TransactionTypeID, TT.TransactionType,   
PT.PAN 'EmbossLine',PT.PreBalanceAmount, PT.PostBalanceAmount, RefTxnID, SettlementDate,PaidCash, CreditAmount, DiscountAmount,  
RefPAN, Remarks, PT.Product,
case PT.Product when 1 then 'Taxi' end 'ProductName'
case PT.Product when 2 then 'Airport Lounge' end 'ProductName'
into #Temp  
from POS_Transactions PT inner join TransactionType TT on TT.TransactionTypeID = PT.TransactionTypeID  
where   
PT.[ID] not in (Select distinct isnull(TransactionID,0) from Testcards)  
and (PT.TransactionDate >= @DateFrom)  
and (PT.TransactionDate < @DateTo)  
and (PT.TransactionTypeID = @TransactionTypeID or @TransactionTypeID = -999)  


select T.*,  C.EmbossLine+'&nbsp;' as 'EmbossLine',  C.EmbossLine as 'EmbossLine1',  
C.EmbossName, PM.MerchantID, PM.MerchantName1, C.AccountNumber, C.VehicleNumber  
from #Temp T   
inner join Card C on C.EmbossLine= T.EmbossLine  
inner join Terminal on Terminal.TerminalID = T.TerminalID  
inner join Merchant PM on  PM.MerchantID = Terminal.MerchantID  
where C.Status <>'E3'  
and C.CardID not in (Select distinct isnull(CardID,0) from Testcards)  
and (PM.MerchantID =@MerchantID or @MerchantID='-999')  
and (C.EmbossLine like '%'+@EmbossLine+'%' or @EmbossLine like '-999')  
and (C.EmbossName like '%'+@EmbossName+'%' or @EmbossName like '-999')  
order by T.TransactionDate, MerchantName1, T.BatchNumber, T.SequenceNumber  


drop table #Temp  

When I create it, command is executed succesfully. However when I call it, it throws following error

Column names in each table must be unique. Column name 'ProductName' in table '#Temp' is specified more than once.

I think I have problem in the syntax in these lines

case PT.Product when 1 then 'Taxi' end 'ProductName'
case PT.Product when 2 then 'Airport Lounge' end 'ProductName'

Can someone identify?

Answer 1

Your line is indeed a problem.
I suspect you're after something like:

case PT.Product 
        when 1 then 'Taxi'
        when 2 then 'Airport Lounge' 
end 'ProductName'

In your syntax you make two different cases, resulting in two columns being selected, both called the same.
Above the case can return two different values into the one row.