SQL Server Update Trigger, Get Only modified fields
https://stackoverflow.com/questions/1254787
-
12-09-2019 - |
italiano
english
français
española
中国
日本の
العربية
Deutsch
한국어
Português
RussianQuestion
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 it)
I need basicaly an XML of only updated column values, I need this for replication purpose.
SELECT * FROM inserted gives me each column, but I need only updated ones.
something like following...
CREATE TRIGGER DBCustomers_Insert
ON DBCustomers
AFTER UPDATE
AS
BEGIN
DECLARE @sql as NVARCHAR(1024);
SET @sql = 'SELECT ';
I NEED HELP FOR FOLLOWING LINE ...., I can manually write every column, but I need
an automated routin which can work regardless of column specification
for each column, if its modified append $sql = ',' + columnname...
SET @sql = $sql + ' FROM inserted FOR XML RAW';
DECLARE @x as XML;
SET @x = CAST(EXEC(@sql) AS XML);
.. use @x
END
Solution
Inside the trigger, you can use COLUMNS_UPDATED() like this in order to get updated value
-- Get the table id of the trigger
--
DECLARE @idTable INT
SELECT @idTable = T.id
FROM sysobjects P JOIN sysobjects T ON P.parent_obj = T.id
WHERE P.id = @@procid
-- Get COLUMNS_UPDATED if update
--
DECLARE @Columns_Updated VARCHAR(50)
SELECT @Columns_Updated = ISNULL(@Columns_Updated + ', ', '') + name
FROM syscolumns
WHERE id = @idTable
AND CONVERT(VARBINARY,REVERSE(COLUMNS_UPDATED())) & POWER(CONVERT(BIGINT, 2), colorder - 1) > 0
But this snipet of code fails when you have a table with more than 62 columns.. Arth.Overflow...
Here is the final version which handles more than 62 columns but give only the number of the updated columns. It's easy to link with 'syscolumns' to get the name
DECLARE @Columns_Updated VARCHAR(100)
SET @Columns_Updated = ''
DECLARE @maxByteCU INT
DECLARE @curByteCU INT
SELECT @maxByteCU = DATALENGTH(COLUMNS_UPDATED()),
@curByteCU = 1
WHILE @curByteCU <= @maxByteCU BEGIN
DECLARE @cByte INT
SET @cByte = SUBSTRING(COLUMNS_UPDATED(), @curByteCU, 1)
DECLARE @curBit INT
DECLARE @maxBit INT
SELECT @curBit = 1,
@maxBit = 8
WHILE @curBit <= @maxBit BEGIN
IF CONVERT(BIT, @cByte & POWER(2,@curBit - 1)) <> 0
SET @Columns_Updated = @Columns_Updated + '[' + CONVERT(VARCHAR, 8 * (@curByteCU - 1) + @curBit) + ']'
SET @curBit = @curBit + 1
END
SET @curByteCU = @curByteCU + 1
END
OTHER TIPS
I've another completely different solution that doesn't use COLUMNS_UPDATED at all, nor does it rely on building dynamic SQL at runtime. (You might want to use dynamic SQL at design time but thats another story.)
Basically you start with the inserted and deleted tables, unpivot each of them so you are just left with the unique key, field value and field name columns for each. Then you join the two and filter for anything that's changed.
Here is a full working example, including some test calls to show what is logged.
-- -------------------- Setup tables and some initial data --------------------
CREATE TABLE dbo.Sample_Table (ContactID int, Forename varchar(100), Surname varchar(100), Extn varchar(16), Email varchar(100), Age int );
INSERT INTO Sample_Table VALUES (1,'Bob','Smith','2295','bs@example.com',24);
INSERT INTO Sample_Table VALUES (2,'Alice','Brown','2255','ab@example.com',32);
INSERT INTO Sample_Table VALUES (3,'Reg','Jones','2280','rj@example.com',19);
INSERT INTO Sample_Table VALUES (4,'Mary','Doe','2216','md@example.com',28);
INSERT INTO Sample_Table VALUES (5,'Peter','Nash','2214','pn@example.com',25);
CREATE TABLE dbo.Sample_Table_Changes (ContactID int, FieldName sysname, FieldValueWas sql_variant, FieldValueIs sql_variant, modified datetime default (GETDATE()));
GO
-- -------------------- Create trigger --------------------
CREATE TRIGGER TriggerName ON dbo.Sample_Table FOR DELETE, INSERT, UPDATE AS
BEGIN
SET NOCOUNT ON;
--Unpivot deleted
WITH deleted_unpvt AS (
SELECT ContactID, FieldName, FieldValue
FROM
(SELECT ContactID
, cast(Forename as sql_variant) Forename
, cast(Surname as sql_variant) Surname
, cast(Extn as sql_variant) Extn
, cast(Email as sql_variant) Email
, cast(Age as sql_variant) Age
FROM deleted) p
UNPIVOT
(FieldValue FOR FieldName IN
(Forename, Surname, Extn, Email, Age)
) AS deleted_unpvt
),
--Unpivot inserted
inserted_unpvt AS (
SELECT ContactID, FieldName, FieldValue
FROM
(SELECT ContactID
, cast(Forename as sql_variant) Forename
, cast(Surname as sql_variant) Surname
, cast(Extn as sql_variant) Extn
, cast(Email as sql_variant) Email
, cast(Age as sql_variant) Age
FROM inserted) p
UNPIVOT
(FieldValue FOR FieldName IN
(Forename, Surname, Extn, Email, Age)
) AS inserted_unpvt
)
--Join them together and show what's changed
INSERT INTO Sample_Table_Changes (ContactID, FieldName, FieldValueWas, FieldValueIs)
SELECT Coalesce (D.ContactID, I.ContactID) ContactID
, Coalesce (D.FieldName, I.FieldName) FieldName
, D.FieldValue as FieldValueWas
, I.FieldValue AS FieldValueIs
FROM
deleted_unpvt d
FULL OUTER JOIN
inserted_unpvt i
on D.ContactID = I.ContactID
AND D.FieldName = I.FieldName
WHERE
D.FieldValue <> I.FieldValue --Changes
OR (D.FieldValue IS NOT NULL AND I.FieldValue IS NULL) -- Deletions
OR (D.FieldValue IS NULL AND I.FieldValue IS NOT NULL) -- Insertions
END
GO
-- -------------------- Try some changes --------------------
UPDATE Sample_Table SET age = age+1;
UPDATE Sample_Table SET Extn = '5'+Extn where Extn Like '221_';
DELETE FROM Sample_Table WHERE ContactID = 3;
INSERT INTO Sample_Table VALUES (6,'Stephen','Turner','2299','st@example.com',25);
UPDATE Sample_Table SET ContactID = 7 where ContactID = 4; --this will be shown as a delete and an insert
-- -------------------- See the results --------------------
SELECT *, SQL_VARIANT_PROPERTY(FieldValueWas, 'BaseType') FieldBaseType, SQL_VARIANT_PROPERTY(FieldValueWas, 'MaxLength') FieldMaxLength from Sample_Table_Changes;
-- -------------------- Cleanup --------------------
DROP TABLE dbo.Sample_Table; DROP TABLE dbo.Sample_Table_Changes;
So no messing around with bigint bitfields and arth overflow problems. If you know the columns you want to compare at design time then you don't need any dynamic SQL.
On the downside the output is in a different format and all the field values are converted to sql_variant, the first could be fixed by pivoting the output again, and the second could be fixed by recasting back to the required types based on your knowledge of the design of the table, but both of these would require some complex dynamic sql. Both of these might not be an issue in your XML output. This question does something similar to getting the output back in the same format.
Edit: Reviewing the comments below, if you have a natural primary key that could change then you can still use this method. You just need to add a column that is populated by default with a GUID using the NEWID() function. You then use this column in place of the primary key.
You may want to add an index to this field, but as the deleted and inserted tables in a trigger are in memory it might not get used and may have a negative effect on performance.
I've done it as simple "one-liner". Without using, pivot, loops, many variables etc. that makes it looking like procedural programming. SQL should be used to process data sets :-), the solution is:
DECLARE @sql as NVARCHAR(1024);
select @sql = coalesce(@sql + ',' + quotename(column_name), quotename(column_name))
from INFORMATION_SCHEMA.COLUMNS
where substring(columns_updated(), columnproperty(object_id(table_schema + '.' + table_name, 'U'), column_name, 'columnId') / 8 + 1, 1) & power(2, -1 + columnproperty(object_id(table_schema + '.' + table_name, 'U'), column_name, 'columnId') % 8 ) > 0
and table_name = 'DBCustomers'
-- and column_name in ('c1', 'c2') -- limit to specific columns
-- and column_name not in ('c3', 'c4') -- or exclude specific columns
SET @sql = 'SELECT ' + @sql + ' FROM inserted FOR XML RAW';
DECLARE @x as XML;
SET @x = CAST(EXEC(@sql) AS XML);
It uses COLUMNS_UPDATED, takes care of more than eight columns - it handles as many columns as you want.
It takes care on proper columns order which should be get using COLUMNPROPERTY.
It is based on view COLUMNS so it may include or exclude only specific columns.
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
The below code works for over 64 columns and logs only the updated columns. Follow the instruction in the comments and all should be well.
/*******************************************************************************************
* Add the below table to your database to track data changes using the trigger *
* below. Remember to change the variables in the trigger to match the table that *
* will be firing the trigger *
*******************************************************************************************/
SET ANSI_NULLS ON;
GO
SET QUOTED_IDENTIFIER ON;
GO
CREATE TABLE [dbo].[AuditDataChanges]
(
[RecordId] [INT] IDENTITY(1, 1)
NOT NULL ,
[TableName] [VARCHAR](50) NOT NULL ,
[RecordPK] [VARCHAR](50) NOT NULL ,
[ColumnName] [VARCHAR](50) NOT NULL ,
[OldValue] [VARCHAR](50) NULL ,
[NewValue] [VARCHAR](50) NULL ,
[ChangeDate] [DATETIME2](7) NOT NULL ,
[UpdatedBy] [VARCHAR](50) NOT NULL ,
CONSTRAINT [PK_AuditDataChanges] PRIMARY KEY CLUSTERED
( [RecordId] 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
ALTER TABLE [dbo].[AuditDataChanges] ADD CONSTRAINT [DF_AuditDataChanges_ChangeDate] DEFAULT (GETDATE()) FOR [ChangeDate];
GO
/************************************************************************************************
* Add the below trigger to any table you want to audit data changes on. Changes will be saved *
* in the AuditChangesTable. *
************************************************************************************************/
ALTER TRIGGER trg_Survey_Identify_Updated_Columns ON Survey --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 = 'Survey'; ---Change to your table name
SELECT @UpdatedBy = UpdatedBy --Change to your column name for the user update field
FROM inserted;
SELECT @RecordPk = SurveyId --Change to the table primary key field
FROM inserted;
SET @RecordPkName = 'SurveyId';
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;
IF ( LTRIM(RTRIM(@NewValue)) != LTRIM(RTRIM(@OldValue)) )
BEGIN
SET @sql = 'INSERT INTO [dbo].[AuditDataChanges]
([TableName]
,[RecordPK]
,[ColumnName]
,[OldValue]
,[NewValue]
,[UpdatedBy])
VALUES
(' + QUOTENAME(@TABLE_NAME, '''') + '
,' + QUOTENAME(@RecordPk, '''') + '
,' + QUOTENAME(@COLUMN_NAME, '''') + '
,' + QUOTENAME(@OldValue, '''') + '
,' + QUOTENAME(@NewValue, '''') + '
,' + QUOTENAME(@UpdatedBy, '''') + ')';
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;
DROP TABLE #Inserted;
DROP TABLE #deleted;
GO
I transformed the accepted answer to get list of column names separated by comma (according to author's recommendation). Output - "Columns_Updated" as 'Column1,Column2,Column5'
-- get names of updated columns
DECLARE @idTable INT
declare @ColumnName nvarchar(300)
declare @ColId int
SELECT @idTable = T.id
FROM sysobjects P JOIN sysobjects T ON P.parent_obj = T.id
WHERE P.id = @@procid
DECLARE @changedProperties nvarchar(max) = ''
DECLARE @Columns_Updated VARCHAR(2000) = ''
DECLARE @maxByteCU INT
DECLARE @curByteCU INT
SELECT @maxByteCU = DATALENGTH(COLUMNS_UPDATED()),
@curByteCU = 1
WHILE @curByteCU <= @maxByteCU BEGIN
DECLARE @cByte INT
SET @cByte = SUBSTRING(COLUMNS_UPDATED(), @curByteCU, 1)
DECLARE @curBit INT
DECLARE @maxBit INT
SELECT @curBit = 1,
@maxBit = 8
WHILE @curBit <= @maxBit BEGIN
IF CONVERT(BIT, @cByte & POWER(2, @curBit - 1)) <> 0 BEGIN
SET @ColId = cast( CONVERT(VARCHAR, 8 * (@curByteCU - 1) + @curBit) as int)
select @ColumnName = [Name]
FROM syscolumns
WHERE id = @idTable and colid = @ColId
SET @Columns_Updated = @Columns_Updated + ',' + @ColumnName
END
SET @curBit = @curBit + 1
END
SET @curByteCU = @curByteCU + 1
END
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;Licensed under: CC-BY-SA with attribution
Not affiliated with StackOverflow
