sql 根据客户需用 增减查询字段

DECLARE @vcFieldName VARCHAR(100)= 'nMerchantId,nUserId,dmMoney'
SELECT  nMerchantId, nUserId, dmMoney, CASE WHEN CHARINDEX('nMerchantId', @vcFieldName) > 0 THEN nMerchantId
                                            ELSE 0
                                       END + CASE WHEN CHARINDEX('nUserId', @vcFieldName) > 0 THEN nUserId
                                                  ELSE 0
                                             END + CASE WHEN CHARINDEX('dmMoney', @vcFieldName) > 0 THEN dmMoney
                                                        ELSE 0
                                                   END AS dmTotal
FROM    GM.CRM_Customer