I am making some tweaks to a legacy application built on SQL Server 2000, needless to say I only want to do the absolute minimum in the fear that it may just all fall apart.
I have a large table of users, tbUsers, with a BIT flag for IsDeleted. I want to archive off all current and future IsDeleted = 1 user records into my archive table tbDeletedUsers.
Moving the currently deleted users is straight forward, however I want a way to move any future users where the IsDeleted flag is set. I could use a standard AFTER trigger on the column however I plan to add some constraints to the tbUser table that would violate this, what I'd like is for my INSTEAD OF UPDATE trigger to fire and move the record to archive table instead?
I guess my question is... is it possible to trigger an INSTEAD OF UPDATE trigger on the update of an individual column? This is what I have so far:
CREATE TRIGGER trg_ArchiveUsers
INSTEAD OF UPDATE ON tbUsers
AS
BEGIN
...
END
GO
If so an example (SQL 2000 compatible) would be much appreciated!
Using the UPDATE(columnname) test, you can check in a trigger whether a specific column was updated (and then take specific actions), but you can't have a trigger fire only on the update of a specific column. It will fire as soon as the update is performed, regardless of the fact which column was the target of the update.
So, if you think you have to use an INSTEAD OF UPDATE trigger, you'll need to implement two kinds of actions in it:
1) insert into tbDeletedUsers + delete from tbUsers – when IsDeleted is updated (or, more exactly, updated and set to 1);
2) update tbUsers normally – when IsDeleted is not updated (or updated but not set to 1).
Because more than one row can be updated with a single UPDATE instruction, you might also need to take into account that some rows might have IsDeleted set to 1 and others not.
I'm not a big fan of INSTEAD OF triggers, but if I really had to use one for a task like yours, I might omit the UPDATE() test and implement the trigger like this:
CREATE TRIGGER trg_ArchiveUsers
ON tbUsers
INSTEAD OF UPDATE
AS
BEGIN
UPDATE tbUsers
SET
column = INSERTED.column,
…
FROM INSERTED
WHERE INSERTED.key = tbUsers.key
AND INSERTED.IsDeleted = 0
;
DELETE FROM tbUsers
FROM INSERTED
WHERE INSERTED.key = tbUsers.key
AND INSERTED.IsDeleted = 1
;
INSERT INTO tbDeletedUsers (columns)
SELECT columns
FROM INSERTED
WHERE IsDeleted = 1
;
END
Related
I have a table where the user is able to insert the ID of a Node that corresponds to a title elsewhere in the database. I want this tile to be automatically inserted into the row after the user has chosen the id.
This is my table:
I need to have the "SommerhusNavn" column be automatically filled with values based on the "SommerhusId" inserted.
I am using a third party to handle the CRUD functionality, where the user picks the ID from a dropdown. I already know in which table the title for the ID is located, I'm just not sure how to fill the row with the insert statement. Would I need to run a separate query for this to happen?
Edit:Solution
CREATE TRIGGER [dbo].[BlokeredePerioderInsert]
ON dbo.BlokeredePerioder
AFTER INSERT
AS
BEGIN
SET NOCOUNT ON;
UPDATE BlokeredePerioder SET SommerhusNavn = text FROM umbracoNode AS umbNode
where SommerhusId = umbNode.id
END
GO
Yes, you need to run additional UPDATE query. Let's assume that you have the TitlesTable, with columns ID and Title. Then it should look like:
UPDATE MyTable SET SommerhusNavn = Title FROM TitlesTable AS A
WHERE SommerhusId = A.ID
AND SommerhusNavn IS NOT NULL --not necessary
Perhaps i'm not understanding, but why can't you use send the value across in the initial update?
Can you use a trigger on the database side?
Alternatively, you'll need to send a update across, following the insert.
Suppose we have table A with fields time: date, status: int, playerId: int, serverid: int
We added constraint on time, playerid and serverid (UNQ_TIME_PLAYERID_SERVERID)
At some time we try to update all rows in table A with new status and date:
update status = 1, time = sysdate where serverid=XXX and status != 1 and time > sysdate
Problem that there are two separated processes on separate machines that can execute same update at same sysdate.
And UNQ_TIME_PLAYERID_SERVERID violation occurs!
Is there any possibility to force Oracle check where cause before concrete update (when lock on row acquired)?
I do not want to use any 'select for update' things
If it's really the same update 100% of the time, then just catch the exception and ignore it.
In case you want to prevent an error occuring in the first place, you need to implement some logic to prevent the second update statement from ever executing.
I could think of a "lock table" just for this purpose. Create a table TABLE_A_LOCK_TB (add columns based on what information you want to have stored there for administrative reasons, e.g. user who set the lock or a timestamp, ...).
Before you execute an update statement on table A, just insert a row to TABLE_A_LOCK_TB. Once an update was successful, delete said row.
Before executing any update statement on table A just check whether the TABLE_A_LOCK_TB has a dataset. If it doesn't your update is good to go, if it does you don't execute the update.
To make this process easier you could just write a package for "locking" and "unlocking" table A by inserting / deleting a row from the TABLE_A_LOCK_TB. Also implement a function to check the "lock status".
If you need this logic for several tables you can also make it dynamic by just having a column holding the table name in TABLE_A_LOCK_TB and checking against that.
In your application logic you can handle every update like this then (pseudocode):
IF your_lock_package.lock_status(table_name) = false THEN
your_lock_package.set_lock(table_name);
-- update statement(s)
your_lock_package.release_lock(table_name);
ELSE
-- "error" handling / information to user + exit
I have never really worked with Triggers before in MSSQL but I think it'll be what I need for this task.
The structure of the table is as such:
ID|****|****|****|****|****|****|****|TOUROPERATOR
The Tour Operator Code is the code that tells us what company owned the flight we carried out for them. Two of those codes (there are 24 in total) are outdated. Our users requested that those two be changed but the tour operator code is pulled from a database we don't control. The FlightData table however, we do control. So I was thinking a trigger could change the tour operator code if it was one of the two outdated ones, to the correct ones instead respectively when they were inserted.
So I went into good ol' SQL Management Studio and asked to make a trigger. It gave me some sample code and here is my Pseudo Code below:
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TRIGGER ChangeProvider
ON FlightData
AFTER INSERT
AS
BEGIN
IF(TheInsertedValue == Criteria)
UPDATE FlightData
SET TheInsertedValue = NewValue
ENDIF
END
GO
I am not that good with this type of Database Programming so excuse my mistakes.
How would I go about doing this?
You could add a computed column to your table instead of adding a trigger.
Then the new column could just use a case statement to either show
the original TourOperator column value or the new value you wanted.
You'd add a new column to your table like this
TourOperatorCorrect = CASE WHEN TourOperator = 'Whatever value' THEN 'ChangedValue'
--I just want to use what I have already in the TourOperator column
ELSE TourOperator
END AS VARCHAR(50)
Basics of computed columns are here - https://msdn.microsoft.com/en-ie/library/ms188300.aspx
Your misconception here is that the trigger runs once per inserted value - it is in fact run once per insert statement, so you can and will find more than one row inserted at once.
You'll find that your inserted values are in the pseudo table inserted, which has the same structure as your FlightData table in this case. You write a select statement against that, specifying any criteria you wish.
However, it's not immediately clear what your logic is - does the FlightData table you are updating in your trigger only have one row? Do you update every row in the table with the newest inserted value? It is hard to understand what you are trying to now, and what the purpose of the table and this trigger are - let alone what you would want to do if you inserted more than one row at once.
When inserted table contains mutiple rows,your code will fail,so change code to work with inserted table as whole
UPDATE F
SET f.TheInsertedValue = i.value
from inserted i
join
Flighttable F
on f.matchingcolumn=i.matchingcolumn
and i.somevalue='criteria'
I want to track the update changes in a table via a trigger:
CREATE TABLE dbo.TrackTable(...columns same as target table)
GO
CREATE TRIGGER dboTrackTable
ON dbo.TargetTable
AFTER UPDATE
AS
INSERT INTO dbo.TrackTable (...columns)
SELECT (...columns)
FROM Inserted
However in real production some of the update queries select rows with vague conditions and update them all regardless of whether they are actually changed, like
UPDATE Targettable
SET customer_type = 'VIP'
WHERE 1 = 1
--or is_obsolete = 0 or register_date < '20160101' something
But due to table size and to analyze, I only want to choose those actually modified data for tracking. How to achieve this goal?
My track table has many columns (so I do not prefer checking inserted and deleted column one by one) but it seldom changes structure.
I guess the following code will be useful.
CREATE TABLE dbo.TrackTable(...columns same as target table)
GO
CREATE TRIGGER dboTrackTable
ON dbo.TargetTable
AFTER UPDATE
AS
INSERT INTO dbo.TrackTable (...columns)
SELECT *
FROM Inserted
EXCEPT
SELECT *
FROM Deleted
I realize this post is a couple months old now, but for anyone looking for a well-rounded answer:
To exit the trigger if no rows were affected on SQL Server 2016 and up, Microsoft recommends using the built-in ROWCOUNT_BIG() function in the Optimizing DML Triggers section of the Create Trigger documentation.
Usage:
IF ROWCOUNT_BIG() = 0
RETURN;
To ensure you are excluding rows that were not changed, you'll need to do a compare of the inserted and deleted tables inside the trigger. Taking your example code:
INSERT INTO dbo.TrackTable (...columns)
SELECT (...columns)
FROM Inserted i
INNER JOIN deleted d
ON d.[SomePrimaryKeyCol]=i.[SomePrimaryKeyCol] AND
i.customer_type<>d.customer_type
Microsoft documentation and w3schools are great resources for learning how to leverage various types of queries and trigger best practices.
Prevent trigger from doing anything if no rows changed.
Writing-triggers-the-right-way
CREATE TRIGGER the_trigger on dbo.Data
after update
as
begin
if ##ROWCOUNT = 0
return
set nocount on
/* Some Code Here */
end
Get a list of rows that changed:
CREATE TRIGGER the_trigger on dbo.data
AFTER UPDATE
AS
SELECT * from inserted
Previous stack overflow on triggers
#anna - as per #Oded's answer, when an update is performed, the rows are in the deleted table with the old information, and the inserted table with the new information –
UPDATE UPI_ATTRIBUTE SET SITE_INC ='0'
WHERE USER_PROFILING_NAME IN ('CAR_IMPLICIT','CAR_EXPLICIT')
Above is my query that I am using to update the columns in UPI_ATTRIBUTE table. And suppose if I need to rollback the above changes that I am doing with update query, then how can I use the delete query in the above case? Currently SITE_INC is empty. So after updating the table it will have 0 in that. And If I need to rollback the changes then I need to make it empty again.
How can I delete the value 0 from above column after updating.
You cannot "delete" data to rollback an update.
Even if the only change that you'll do is set a flag from "NULL" to "Y" and vice versa, you can't really determine which value to update when you do multiple updates.
update 1 : set from "NULL" to "0"
update 2 : set from "0" to "something else"
update 3 : Rollback changes (rollback to which state)?
If you want to really rollback changes to specific rows (instead of the complete table, which can be done using Flashback), you can audit the changes to "remember" the values and then revert back to them.
Even then, you should consider which point to revert to, when you have multiple updates.
Not sure Oracle have final table/old table function for select/update.
For DB2 for z/OS, it have such function:
SELECT LASTNAME, BONUS FROM FINAL TABLE
(UPDATE EMP SET BONUS = BONUS * 1.3
WHERE JOB = 'CLERK');
Then, the result set of the select include all the updated rows. you can use rownum or other unique value, then you can update it back to any value as you want.