如何添加"IF NOT EXISTS"来创建触发器语句

Question

我正在使用sql server 2008 R2.更具体地说,Microsoft SQL Server 2008 R2(RTM) - 10.50.1600.1(X64)2010年4月2日15:48:46版权所有(c)Windows NT 6.1上的Microsoft Corporation标准版(64位)(Build 7601:Service Pack 1) )(管理程序).我是sql server和procedures/triggers的新手.我有以下代码来创建一个触发器(它工作):

CREATE TRIGGER [dbo].[Insert_WithdrawalCodes] 
   ON  [dbo].[PupilWithdrawalReason] 
   AFTER INSERT
AS 
BEGIN
    SET NOCOUNT ON;
        UPDATE [dbo].[PupilWithdrawalReason] SET DateCreated=dbo.SYSTEMTIME() 
        WHERE WithdrawalCodeID IN (SELECT WithdrawalCodeID FROM inserted)
END

仅当触发器尚不存在时,如何有条件地创建？我在这做错了什么？Stackoverflow有很好的"如果不存在"的例子,但我不能让它与CREATE一起工作.这是我失败的努力之一:

IF NOT EXISTS (SELECT * FROM sys.objects WHERE type = 'TR' AND name = 'Insert_WithdrawalCodes')
   exec('CREATE TRIGGER [dbo].[Insert_WithdrawalCodes] ON  [dbo].[PupilWithdrawalReason] AFTER INSERT AS BEGIN SET NOCOUNT ON; UPDATE [dbo].[PupilWithdrawalReason] SET DateCreated=dbo.SYSTEMTIME() WHERE WithdrawalCodeID IN (SELECT WithdrawalCodeID FROM inserted) END')
GO

Answer 1

IF EXISTS (SELECT * FROM sys.triggers WHERE object_id = OBJECT_ID(N'[dbo].[TRIGGERNAME]'))
DROP TRIGGER [dbo].[TRIGGERNAME]
go
IF  EXISTS (SELECT * FROM dbo.sysobjects WHERE id = OBJECT_ID(N'[dbo].[TABLENAME]') AND OBJECTPROPERTY(id, N'IsUserTable') = 1)
BEGIN
CREATE   TRIGGER [dbo].[TRIGGERNAME] ON [dbo].[TABLENAME] FOR INSERT, UPDATE 

AS ...

END

根据您更新的问题...试试这个:

IF NOT EXISTS (select * from sys.objects where type = 'TR' and name = 'Insert_WithdrawalCodes')
EXEC dbo.sp_executesql @statement = N'

CREATE TRIGGER [dbo].[Insert_WithdrawalCodes] 
   ON  [dbo].[PupilWithdrawalReason] 
   AFTER INSERT
AS 
BEGIN
    SET NOCOUNT ON;
        UPDATE [dbo].[PupilWithdrawalReason] SET DateCreated=dbo.SYSTEMTIME() 
        WHERE WithdrawalCodeID IN (SELECT WithdrawalCodeID FROM inserted)
END


 '

Answer 2

最好的方法是检查对象,如果它们存在则删除它们,然后再创建它们.

而不是在它存在的情况下根本不创建它,我会以另一种方式接近它,如果存在则删除它然后创建.

通常在长长度脚本中,如果要更新触发器的定义,只需在该脚本的末尾添加它,并更新触发器定义.

所以方法应该是create the object but drop it if it already exists而不是dont create it at all if it already exists

IF OBJECT_ID ('[Insert_WithdrawalCodes] ', 'TR') IS NOT NULL
   DROP TRIGGER [Insert_WithdrawalCodes];
GO

CREATE TRIGGER .......

Answer 3

像CREATE TRIGGER这样的某些语句需要成为批处理中的第一个语句(例如,由GO分隔的语句组).

https://msdn.microsoft.com/en-us/library/ms175502.aspx

或者你可以这样做

IF NOT EXISTS ( SELECT  *
            FROM    sys.objects
            WHERE   type = 'TR'
                    AND name = 'Insert_WithdrawalCodes' ) 
BEGIN
    EXEC ('CREATE TRIGGER Insert_WithdrawalCodes ON ...');
END;

Answer 4

由于上面的其他答案没有提到一个重点，我写了这个答案：

• 当我们想在sys.objects表中查找触发器或其他对象时，最好object_id在 where 子句中准确检查（使用 schema 或等），以避免同名无效结果。考虑当另一个模式中已经存在另一个同名触发器......因此，因为该sys.object表包含一个schema_id列，我们可以使用它name和type列一起使用它来更准确地查询，如下面的示例所示。

• 正如此处在“触发器限制”下提到的 Microsoft 文档：

CREATE TRIGGER 必须是批处理中的第一条语句，并且只能应用于一个表。

因此我们使用EXECUTE来克服这个限制：

IF NOT EXISTS (select * from sys.objects where schema_id=SCHEMA_ID('dbo') AND type='TR' and name='Insert_WithdrawalCodes')
BEGIN
   EXECUTE ('CREATE TRIGGER [Insert_WithdrawalCodes] ON [dbo].[PupilWithdrawalReason]
   AFTER INSERT
   AS 
   BEGIN
      SET NOCOUNT ON;
      ...
   END');
END