SQL服務器檢查爲空值

Question

我有一個表，我添加一個約束，所以如果PaymentType不同於'檢查'，以確保CheckNumber爲null。這是我的表：

create table RegistrationHeader(
    RegistrationNo numeric 
    ,BillingID varchar(30) unique not null 
    ,RegistrationDate date not null 
    ,PaymentType varchar(5) check (PaymentType = 'CC' or PaymentType = 'PO' or PaymentType = 'Check') not null 
    ,CCNumber varchar(16) check(LEN(CCNumber) = 16 OR LEN(CCNumber) = 15) 
    ,PONumber varchar(30) 
    ,CheckNumber varchar(10) default null 
    ,primary key(RegistrationNo) 
    ,constraint CC_CCNumber_constr check(
     (PaymentType = 'CC' and CCNumber is not null) 
     or 
     (PaymentType != 'CC' and CCNumber is null) 
    ) 
    ,constraint PO_PONumber_constr check(
     (PaymentType = 'PO' and (PONumber is not null or PONumber != '')) 
     or 
     (PaymentType != 'PO' and PONumber is null) 
    ) 
); 

所以，我已經試過

,constraint CheckNumber_type_constr check((PaymentType = 'CC' or PaymentType = 'PO') and CheckNumber is null) 

和

,constraint CheckNumber_type_constr check((PaymentType != 'Check') and CheckNumber is null) 

兩者慘遭失敗...

Answer 1

如何：

constraint CheckNumber_type_constr 
    check ((PaymentType = 'Check') or (CheckNumber is null)) 

如果您想確保CheckNumber對於支票不爲空：

constraint CheckNumber_type_constr 
    check ((PaymentType = 'Check' and CheckNumber is not null) or 
      (PaymentType <> 'Check' and CheckNumber is null) 
     )