Log record changes in SQL server in an audit table

1) Create AUDIT Table.

IF NOT EXISTS
      (SELECT * FROM sysobjects WHERE id = OBJECT_ID(N'[dbo].[Audit]')
               AND OBJECTPROPERTY(id, N'IsUserTable') = 1)
       CREATE TABLE Audit
               (Type CHAR(1),
               TableName VARCHAR(128),
               PK VARCHAR(1000),
               FieldName VARCHAR(128),
               OldValue VARCHAR(1000),
               NewValue VARCHAR(1000),
               UpdateDate datetime,
               UserName VARCHAR(128))
GO


2) CREATE an UPDATE Trigger on the GUESTS Table as follows.

CREATE TRIGGER TR_GUESTS_AUDIT ON GUESTS FOR UPDATE
AS

DECLARE @bit INT ,
       @field INT ,
       @maxfield INT ,
       @char INT ,
       @fieldname VARCHAR(128) ,
       @TableName VARCHAR(128) ,
       @PKCols VARCHAR(1000) ,
       @sql VARCHAR(2000), 
       @UpdateDate VARCHAR(21) ,
       @UserName VARCHAR(128) ,
       @Type CHAR(1) ,
       @PKSelect VARCHAR(1000)


--You will need to change @TableName to match the table to be audited. 
-- Here we made GUESTS for your example.
SELECT @TableName = 'GUESTS'

-- date and user
SELECT         @UserName = SYSTEM_USER ,
       @UpdateDate = CONVERT (NVARCHAR(30),GETDATE(),126)

-- Action
IF EXISTS (SELECT * FROM inserted)
       IF EXISTS (SELECT * FROM deleted)
               SELECT @Type = 'U'
       ELSE
               SELECT @Type = 'I'
ELSE
       SELECT @Type = 'D'

-- get list of columns
SELECT * INTO #ins FROM inserted
SELECT * INTO #del FROM deleted

-- Get primary key columns for full outer join
SELECT @PKCols = COALESCE(@PKCols + ' and', ' on') 
               + ' i.' + c.COLUMN_NAME + ' = d.' + c.COLUMN_NAME
       FROM    INFORMATION_SCHEMA.TABLE_CONSTRAINTS pk ,

              INFORMATION_SCHEMA.KEY_COLUMN_USAGE c
       WHERE   pk.TABLE_NAME = @TableName
       AND     CONSTRAINT_TYPE = 'PRIMARY KEY'
       AND     c.TABLE_NAME = pk.TABLE_NAME
       AND     c.CONSTRAINT_NAME = pk.CONSTRAINT_NAME

-- Get primary key select for insert
SELECT @PKSelect = COALESCE(@PKSelect+'+','') 
       + '''<' + COLUMN_NAME 
       + '=''+convert(varchar(100),
coalesce(i.' + COLUMN_NAME +',d.' + COLUMN_NAME + '))+''>''' 
       FROM    INFORMATION_SCHEMA.TABLE_CONSTRAINTS pk ,
               INFORMATION_SCHEMA.KEY_COLUMN_USAGE c
       WHERE   pk.TABLE_NAME = @TableName
       AND     CONSTRAINT_TYPE = 'PRIMARY KEY'
       AND     c.TABLE_NAME = pk.TABLE_NAME
       AND     c.CONSTRAINT_NAME = pk.CONSTRAINT_NAME

IF @PKCols IS NULL
BEGIN
       RAISERROR('no PK on table %s', 16, -1, @TableName)
       RETURN
END

SELECT         @field = 0, 
       @maxfield = MAX(ORDINAL_POSITION) 
       FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = @TableName
WHILE @field < @maxfield
BEGIN
       SELECT @field = MIN(ORDINAL_POSITION) 
               FROM INFORMATION_SCHEMA.COLUMNS 
               WHERE TABLE_NAME = @TableName 
               AND ORDINAL_POSITION > @field
       SELECT @bit = (@field - 1 )% 8 + 1
       SELECT @bit = POWER(2,@bit - 1)
       SELECT @char = ((@field - 1) / 8) + 1
       IF SUBSTRING(COLUMNS_UPDATED(),@char, 1) & @bit > 0
                                       OR @Type IN ('I','D')
       BEGIN
               SELECT @fieldname = COLUMN_NAME 
                       FROM INFORMATION_SCHEMA.COLUMNS 
                       WHERE TABLE_NAME = @TableName 
                       AND ORDINAL_POSITION = @field
               SELECT @sql = '
INSERT INTO AUDIT (    Type, 
               TableName, 
               PK, 
               FieldName, 
               OldValue, 
               NewValue, 
               UpdateDate, 
               UserName)
select ''' + @Type + ''',''' 
       + @TableName + ''',' + @PKSelect
       + ',''' + @fieldname + ''''
       + ',convert(varchar(1000),d.' + @fieldname + ')'
       + ',convert(varchar(1000),i.' + @fieldname + ')'
       + ',''' + @UpdateDate + ''''
       + ',''' + @UserName + ''''
       + ' from #ins i full outer join #del d'
       + @PKCols
       + ' where i.' + @fieldname + ' <> d.' + @fieldname 
       + ' or (i.' + @fieldname + ' is null and  d.'
                                + @fieldname
                                + ' is not null)' 
       + ' or (i.' + @fieldname + ' is not null and  d.' 
                                + @fieldname
                                + ' is null)' 
               EXEC (@sql)
       END
END


GO