在使用transact-SQL删除触发器之前

Question

我需要阻止删除职业为'程序员'的用户。 因此，数据库表结构是：

TABLE Client 
Id | Name | SSN | Occupation | Birthdate | 

我到目前为止创建触发看起来是这样的：

CREATE TRIGGER Check_User_Occupation 
ON dbo.Client 
FOR DELETE 
AS 
BEGIN 
    IF(SELECT c.Occupation 
    FROM deleted AS d 
    INNER JOIN Client as c ON d.Id = c.Id) = 'Programmer' 
    BEGIN 
     PRINT 'YES'; 
     ROLLBACK TRAN 
     RAISEERROR(SELECT 'Could not delete client because he is a programmer'); 
END 
END 
GO 

我想它可以比之前该行被删除，但我不不知道解决这个问题的正确方法。

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Answer 1

正确的语法是在这里：

（你不需要加入删除表，表本身，在删除的是整排的delete语句......）但是要注意一个事实，那你是不是能够做到在这种情况下批量删除。它只能用于行删除。

CREATE TRIGGER Check_User_Occupation 
ON dbo.Client 
FOR DELETE 
AS 
BEGIN 
    IF(SELECT Occupation FROM deleted) = 'Programmer' 
    BEGIN 
     PRINT 'YES'; 

     ROLLBACK 

     RAISERROR ('Could not delete client because he is a programmer', -- Message text 
        16, -- Severity 
        1 -- State 
        ) 

    END 
END 
GO 

对于批处理命令，最好使用有如下语句：

IF(SELECT COUNT(*) FROM deleted WHERE Occupation = 'Programmer') > 0 

但OFC如果你想加入这个表，你需要使用

INSTEAD OF DELETE 

而在这你不需要使用ROLLBACK

Finnaly它应该看起来像：

CREATE TRIGGER Check_User_Occupation 
ON dbo.Client 
INSTEAD OF DELETE 
AS 
BEGIN 
    IF(SELECT Occupation FROM deleted) = 'Programmer' 
    BEGIN 
     PRINT 'YES';   

     RAISERROR ('Could not delete client because he is a programmer', -- Message text 
        16, -- Severity 
        1 -- State 
        ) 

    END 
END 
GO