为另一个选择选择声明的键

(CASE WHEN Status IN ('Selection Process','Approved','Closed') THEN
    CASE WHEN TotalLayerApproval=1 THEN ApprDate1 ELSE
        CASE WHEN TotalLayerApproval=2 THEN ApprDate2 ELSE 
            CASE WHEN TotalLayerApproval=3 THEN ApprDate3 ELSE 
                CASE WHEN TotalLayerApproval=4 THEN ApprDate4 ELSE 
                    CASE WHEN TotalLayerApproval=5 THEN ApprDate5 ELSE 
                        CASE WHEN TotalLayerApproval=6 THEN ApprDate6 ELSE 
                            CASE WHEN TotalLayerApproval=7 THEN ApprDate7 ELSE 
                                CASE WHEN TotalLayerApproval=8 THEN ApprDate8 ELSE 
                                    CASE WHEN TotalLayerApproval=9 THEN ApprDate9 ELSE NULL END
                                END 
                            END 
                        END 
                    END 
                END 
            END 
        END 
    END
ELSE NULL END) AS Date_Approved,
(CASE WHEN Date_Approved IS NULL THEN NULL 
ELSE DATEDIFF(day,Date_Approved, CONVERT(date,GETDATE())) END) AS SLA

例如,如上所述( Date_Approved ),或者有人能再次简化它,这样就不会有太多的案例了