SQL Server Update Trigger, Get Only modified fields

Question

I am aware of COLUMNS_UPDATED, well I need some quick shortcut (if anyone has made, I am already making one, but if anyone can save my time, I will appriciate i

Answer 1

The only way that occurs to me that you could accomplish this without hard coding column names would be to drop the contents of the deleted table to a temp table, then build a query based on the table definition to to compare the contents of your temp table and the actual table, and return a delimited column list based on whether they do or do not match. Admittedly, the below is elaborate.

Declare @sql nvarchar(4000)
DECLARE @ParmDefinition nvarchar(500)
Declare @OutString varchar(8000)
Declare @tbl sysname

Set @OutString = ''
Set @tbl = 'SomeTable' --The table we are interested in
--Store the contents of deleted in temp table
Select * into #tempDelete from deleted 
--Build sql string based on definition 
--of table 
--to retrieve the column name
--or empty string
--based on comparison between
--target table and temp table
set @sql = ''
Select @sql = @sql + 'Case when IsNull(i.[' + Column_Name + 
'],0) = IsNull(d.[' + Column_name + '],0) then '''' 
 else ' + quotename(Column_Name, char(39)) + ' + '',''' + ' end +'
from information_schema.columns 
where table_name = @tbl
--Define output parameter
set @ParmDefinition = '@OutString varchar(8000) OUTPUT'
--Format sql
set @sql = 'Select @OutString = ' 
+ Substring(@sql,1 , len(@sql) -1) + 
' From SomeTable i  ' --Will need to be updated for target schema
+ ' inner join #tempDelete d on
i.PK = d.PK ' --Will need to be updated for target schema
--Execute sql and retrieve desired column list in output parameter
exec sp_executesql @sql, @ParmDefinition, @OutString OUT
drop table  #tempDelete
--strip trailing column if a non-zero length string 
--was returned
if Len(@Outstring) > 0 
    Set @OutString = Substring(@OutString, 1, Len(@Outstring) -1)
--return comma delimited list of changed columns. 
Select @OutString 
End

Answer 2

The sample code provided by Rick lack handling for multiple rows update.

Please let me enhance Rick's version as below:

USE [AFC]
GO

/****** Object:  Trigger [dbo].[trg_Survey_Identify_Updated_Columns]    Script Date: 27/7/2018 14:08:49 ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

ALTER TRIGGER [dbo].[trg_Survey_Identify_Updated_Columns] ON [dbo].[Sample_Table] --Change to match your table name
FOR INSERT
	,UPDATE
AS
SET NOCOUNT ON;

DECLARE @sql VARCHAR(5000)
	,@sqlInserted NVARCHAR(500)
	,@sqlDeleted NVARCHAR(500)
	,@NewValue NVARCHAR(100)
	,@OldValue NVARCHAR(100)
	,@UpdatedBy VARCHAR(50)
	,@ParmDefinitionD NVARCHAR(500)
	,@ParmDefinitionI NVARCHAR(500)
	,@TABLE_NAME VARCHAR(100)
	,@COLUMN_NAME VARCHAR(100)
	,@modifiedColumnsList NVARCHAR(4000)
	,@ColumnListItem NVARCHAR(500)
	,@Pos INT
	,@RecordPk VARCHAR(50)
	,@RecordPkName VARCHAR(50);

SELECT *
INTO #deleted
FROM deleted;

SELECT *
INTO #Inserted
FROM inserted;

SET @TABLE_NAME = 'Sample_Table';---Change to your table name

DECLARE t_cursor CURSOR
FOR
SELECT ContactID 
FROM inserted

OPEN t_cursor

FETCH NEXT
FROM t_cursor
INTO @RecordPk 

WHILE @@FETCH_STATUS = 0
BEGIN
	--SELECT @UpdatedBy = Surname --Change to your column name for the user update field
	--FROM inserted;
	--SELECT @RecordPk = ContactID --Change to the table primary key field
	--FROM inserted;
	SET @RecordPkName = 'ContactID';
	SET @modifiedColumnsList = STUFF((
				SELECT ',' + name
				FROM sys.columns
				WHERE object_id = OBJECT_ID(@TABLE_NAME)
					AND SUBSTRING(COLUMNS_UPDATED(), ((column_id - 1) / 8 + 1), 1) & (POWER(2, ((column_id - 1) % 8 + 1) - 1)) = POWER(2, (column_id - 1) % 8)
				FOR XML PATH('')
				), 1, 1, '');

	WHILE LEN(@modifiedColumnsList) > 0
	BEGIN
		SET @Pos = CHARINDEX(',', @modifiedColumnsList);

		IF @Pos = 0
		BEGIN
			SET @ColumnListItem = @modifiedColumnsList;
		END;
		ELSE
		BEGIN
			SET @ColumnListItem = SUBSTRING(@modifiedColumnsList, 1, @Pos - 1);
		END;

		SET @COLUMN_NAME = @ColumnListItem;
		SET @ParmDefinitionD = N'@OldValueOut NVARCHAR(100) OUTPUT';
		SET @ParmDefinitionI = N'@NewValueOut NVARCHAR(100) OUTPUT';
		SET @sqlDeleted = N'SELECT @OldValueOut=' + @COLUMN_NAME + ' FROM #deleted where ' + @RecordPkName + '=' + CONVERT(VARCHAR(50), @RecordPk);
		SET @sqlInserted = N'SELECT @NewValueOut=' + @COLUMN_NAME + ' FROM #Inserted where ' + @RecordPkName + '=' + CONVERT(VARCHAR(50), @RecordPk);

		EXECUTE sp_executesql @sqlDeleted
			,@ParmDefinitionD
			,@OldValueOut = @OldValue OUTPUT;

		EXECUTE sp_executesql @sqlInserted
			,@ParmDefinitionI
			,@NewValueOut = @NewValue OUTPUT;

		--PRINT @newvalue
		--PRINT @oldvalue

		IF (LTRIM(RTRIM(@NewValue)) != LTRIM(RTRIM(@OldValue)))
		BEGIN
			SET @sql = 'INSERT INTO [dbo].[AuditDataChanges]
                                               ([TableName]
                                               ,[RecordPK]
                                               ,[ColumnName]
                                               ,[OldValue]
                                               ,[NewValue] )
                                         VALUES
                                               (' + QUOTENAME(@TABLE_NAME, '''') + '
                                               ,' + QUOTENAME(@RecordPk, '''') + '
                                               ,' + QUOTENAME(@COLUMN_NAME, '''') + '
                                               ,' + QUOTENAME(@OldValue, '''') + '
                                               ,' + QUOTENAME(@NewValue, '''') + '
                                               '  + ')';

			EXEC (@sql);
		END;

		SET @COLUMN_NAME = '';
		SET @NewValue = '';
		SET @OldValue = '';

		IF @Pos = 0
		BEGIN
			SET @modifiedColumnsList = '';
		END;
		ELSE
		BEGIN
			-- start substring at the character after the first comma
			SET @modifiedColumnsList = SUBSTRING(@modifiedColumnsList, @Pos + 1, LEN(@modifiedColumnsList) - @Pos);
		END;
	END;

	FETCH NEXT
	FROM t_cursor
	INTO @RecordPk 
END

DROP TABLE #Inserted;

DROP TABLE #deleted;

CLOSE t_cursor;

DEALLOCATE t_cursor;