Want to protect your cyber security and still get fast solutions? Ask a secure question today.Go Premium

x
  • Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 434
  • Last Modified:

Help in writing trigger

Hi I have two tables.

Table1
Client_ID int Identity    (PK)

ClientName Varchar(50)
gender Bit
Address varchar(300)
Status char(1)

and a Log table

Table_History

History_ID int Identity(1,1) (PK)

User_ID   int
FieldEffected varchar
Olddata varchar
newdata varchar
timestamp datetime

can any one help me in writing trigger for Insert , Update and delete . for timebeing I can fix user_ID as '1000001'
0
Vikash p
Asked:
Vikash p
  • 2
3 Solutions
 
Brendt HessSenior DBACommented:
In this case, you would do better with three triggers rather than only one.

On your AFTER INSERT trigger, you know every column was changed.  You have the option of logging each item into the table separately, or entering a special row where FieldEffected could equal INSERT, ALL (INSERT), or some other specific value you choose.  OldData would be NULL, and newData would be something like:

Cast(@@Identity as varchar(10) ) + '|' + IsNull(i.ClientName, '') + '|' + Cast(i.gender as char(1)) + '|' + ....  Until you have all of the fields appended into one string.  This is simple.  However, having one item per field is cleaner, so you may decide to simply explicitly code each separate insert into the trigger.  An almost identical procedure could be created for a AFTER DELETE trigger as well.

It only gets complex on an update trigger.

There are various ways that you could try to automate the trigger so that you would always include each field in the table.  Iterating through the correct system view would let you automatically generate the INSERT statements.  However, for this example, I am assuming fixed code for the query.

There are two primary ways to identify if a column has changed (three, if you count a direct compare between INSERTED and DELETED).  The simplest to understand is the UPDATE() function, e.g.

IF UPDATE(ClientName)
... add logging code here ...

IF UPDATE(Gender)
....

Note that the documentation indicates that UPDATE() will return TRUE even if the update failed (that is, nothing changed).

There is also the COLUMNS_UPDATED() function, that returns a bit pattern indicating which columns changed (if any). This returns a VARBINARY containing enough bits so that there is one bit per column in the table.  If you performed an UPDATE on the sample table snippet:


Client_ID int Identity    (PK)
ClientName Varchar(50)
gender Bit
Address varchar(300)
Status char(1)

You would get a bit pattern like:

000 -- There are only five fields, so the last three bits per byte are useless
0     -- Status not updated
1     -- address updated
0     -- gender not updated
1     -- Client Name updated
0     -- Normally, you will not be updating the ID

However you determine it, when you identify the changed columns, you then do a simple INSERT into your log with the appropriate data.
0
 
Anthony PerkinsCommented:
You may want to rethink the design.  However if that is not an option then something like this should do it:
CREATE TRIGGER trg_YourTrigger ON Table1 
	AFTER INSERT, UPDATE, DELETE 

AS

BEGIN

IF UPDATE(ClientName)
	INSERT Table_History ([User_ID], FieldEffected, Olddata, newdata, [timestamp])
	SELECT  '1000001', 'ClientName', d.ClientName, i.ClientName, GETDATE()
	FROM	DELETED d
			FULL OUTER JOIN INSERTED i ON d.Client_ID = i.Client_ID
	WHERE	d.Client_ID IS NULL				-- INSERT
			OR i.Client_ID IS NULL			-- DELETE
			OR d.ClientName <> i.ClientName	-- UPDATE and the values changed

IF UPDATE(gender)
	INSERT Table_History ([User_ID], FieldEffected, Olddata, newdata, [timestamp])
	SELECT  '1000001', 'gender', d.gender, i.gender, GETDATE()
	FROM	DELETED d
			FULL OUTER JOIN INSERTED i ON d.Client_ID = i.Client_ID
	WHERE	d.Client_ID IS NULL				-- INSERT
			OR i.Client_ID IS NULL			-- DELETE
			OR d.gender <> i.gender			-- UPDATE and the values changed

IF UPDATE([Address])
	INSERT Table_History ([User_ID], FieldEffected, Olddata, newdata, [timestamp])
	SELECT  '1000001', 'Address', d.[Address], i.[Address], GETDATE()
	FROM	DELETED d
			FULL OUTER JOIN INSERTED i ON d.Client_ID = i.Client_ID
	WHERE	d.Client_ID IS NULL				-- INSERT
			OR i.Client_ID IS NULL			-- DELETE
			OR d.[Address] <> i.[Address]	-- UPDATE and the values changed

IF UPDATE([Status])
	INSERT Table_History ([User_ID], FieldEffected, Olddata, newdata, [timestamp])
	SELECT  '1000001', 'Status', d.[Status], i.[Status], GETDATE()
	FROM	DELETED d
			FULL OUTER JOIN INSERTED i ON d.Client_ID = i.Client_ID
	WHERE	d.Client_ID IS NULL				-- INSERT
			OR i.Client_ID IS NULL			-- DELETE
			OR d.[Status] <> i.[Status]		-- UPDATE and the values changed
END

Open in new window

0
 
Anthony PerkinsCommented:
Note that the documentation indicates that UPDATE() will return TRUE even if the update failed (that is, nothing changed).
It will always be true if the column participated in an UPDATE statement, regardless of whether the value changed or not.  So really the only way to truly know if the value changed is to compare the values in Deleted and Inserted.
0
 
Scott PletcherSenior DBACommented:
When you compare the old and new values, you also need to compare correctly to allow NULL value(s) to be on one side or the other or both.
0

Featured Post

What does it mean to be "Always On"?

Is your cloud always on? With an Always On cloud you won't have to worry about downtime for maintenance or software application code updates, ensuring that your bottom line isn't affected.

  • 2
Tackle projects and never again get stuck behind a technical roadblock.
Join Now