SELECT中的case语句

Question

ALTER PROCEDURE Transform.usp_CustomerInfo
AS
BEGIN
    TRUNCATE TABLE [Transform].[CustomerInfo]

    INSERT INTO [Transform].[CustomerInfo] (CustomerName, Total, AvgPurchaseTime, StoreName)
        SELECT
            CASE
               WHEN C.LastName = NULL THEN C.FirstName
               ELSE (C.LastName + ', ' + C.FirstName)
            END AS 'Name', 
            SUM(T.Total),
            D.FullDate,
            UPPER(C.StoreName) AS 'Store Name'
        FROM 
            [Extract].[DimTransaction] AS T
        JOIN 
            [Extract].[DimCustomer] AS C ON T.CustomerID = C.CustomerID
        JOIN 
            [Extract].[DimState] AS S ON C.StateID = S.StateID
        JOIN 
            [Extract].[DimDateTime] AS D ON D.DateTimeID = T.TransactionID
        GROUP BY 
            C.LastName, C.FirstName, D.FullDate, C.StoreName
        ORDER BY 
            Convert(date, D.FullDate, 101) ASC

I am trying to get it where if the Last Name comes up NULL to only use the first name else I want to concatenate Last Name and First Name

Answer 1

You can write this as:

(CASE WHEN C.LastName IS NULL THEN C.FirstName
      ELSE (C.LastName + ', ' + C.FirstName)
 END) AS Name, 

Or just use COALESCE() :

(COALESE(C.LastName + ', ', '') + C.FirstName) as Name

Answer 2

NULL is not a value, so it can't use =,<,> to compare with other value. BTW, your case when statement also can do with ISNULL

ISNULL(C.LastName + ', ','')+c.FirstName AS Name

Answer 3

You can't check as = NULL but you can check the default value instead, in the following way or you have to in the way that others suggested:

CASE WHEN ISNULL(c.lastName,'') = '' THEN 
    -------
ELSE
    -------
END

IF you are using SQLSERVER2008+ then you can use CONCAT as well:

CONCAT(ISNULL(c.lastname + ', ',''), c.firstname) as Name