判断字段是否被更新 新旧数据写入Audit Log表中

Audit
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
SET ANSI_PADDING ON
GO
CREATE TABLE [dbo].[Audit](
[Audit_nbr] [int] IDENTITY(1,1) NOT NULL,
[AuditType] [char](1) NOT NULL,
[TableName] [nvarchar](128) NOT NULL,
[FieldName] [nvarchar](128) NULL,
[OldValue] [nvarchar](4000) NULL,
[NewValue] [nvarchar](4000) NULL,
[UserName] [nvarchar](128) NULL,
[CreateDate] [datetime] NOT NULL,
PRIMARY KEY CLUSTERED
(
[Audit_nbr] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
SET ANSI_PADDING OFF
GO
ALTER TABLE [dbo].[Audit] WITH CHECK ADD CHECK (([AuditType]='D' OR [AuditType]='U' OR [AuditType]='I'))
GO
ALTER TABLE [dbo].[Audit] ADD DEFAULT (getdate()) FOR [CreateDate]
GO

--@N和@O两个变量，一个存储更新数据值，一个为原有数据值
DECLARE @sql NVARCHAR(MAX),@N DECIMAL(18,0),@O DECIMAL(18,0)
--@I变量是用户需要跟踪的字段
SET @sql = N'SELECT @N = ['+ CONVERT(NVARCHAR(MAX),@I) +'] FROM #inserted'
--执行动态SQL语句。
EXECUTE sp_executesql @sql,
N'@N DECIMAL(18,0) OUTPUT',
@N OUTPUT;
--下面SQL代码，是从deleted表中获取原来数据值。
SET @sql = N'SELECT @O = ['+ CONVERT(NVARCHAR(MAX),@I) +'] FROM #deleted'
EXECUTE sp_executesql @sql,
N'@O DECIMAL(18,0) OUTPUT',
@O OUTPUT;
--对比两个数据值，更新值与原有值，如果不一样，把数据插入Audit Log表中。
IF (ISNULL(@N,0) <> ISNULL(@O,0))
EXECUTE [dbo].[usp_Audit_Insert] 'U','<tableName>','<fieldName>',@O,@N,@UserName

usp_Audit_Insert
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER PROCEDURE [dbo].[usp_Audit_Insert]
(
@AuditType [char](1),
@TableName [nvarchar](128),
@FieldName [nvarchar](128),
@OldValue [nvarchar](4000),
@NewValue [nvarchar](4000),
@UserName [nvarchar](128)
)
AS
INSERT INTO [dbo].[Audit]
([AuditType],[TableName],[FieldName],[OldValue],[NewValue],[UserName])
VALUES
(@AuditType,@TableName,@FieldName,@OldValue,@NewValue,@UserName)