I’m trying to create a trigger to change the value of a column in table B if it finds the information in a column in table A.
An example of my database is below:
[TableA],
itemID
[TableB],
itemID
itemInStock
Once a user creates an entry in Table A declaring an itemID, the trigger needs to change the TableB.itemInStock column to ‘Yes’
I’m still learning SQL so excuse me if I’ve missed something, let me know if you need any more info.
I understand there are better ways of doing this but I've been told I need to do this using a trigger.
I've attempted a few different things, but as it stands nothing is working, below is the current solution I have however this updates all itemInStock rows to 'Yes', where as I only want the ones to update where the TableB.itemID matches the itemID entered in TableA.
ALTER TRIGGER [itemAvailability] ON [dbo].[TableA] FOR
INSERT
AS
BEGIN
UPDATE [dbo].[TableB] set itemInStock = 'Yes' WHERE
TableB.itemID = itemID
END
Two problems -
you're not looking at the Inserted pseudo table which contains the
newly inserted rows
you're assuming the trigger is called once per row - this is not the
case, the trigger is called once per statement and the Inserted
pseudo table will contain multiple rows - and you need to deal with
that
So, your code should look like this -
ALTER TRIGGER [itemAvailability] ON [dbo].[TableA]
FOR INSERT
AS
UPDATE TB
SET itemInStock = 'Yes'
FROM [dbo].[TableB] TB JOIN inserted I
on TB.itemID = I.itemID
I have a table called dsReplicated.matDB and a column fee_earner. When that column is updated, I want to record two pieces of information:
dsReplicated.matDB.mt_code
dsReplicated.matDB.fee_earner
from the row where fee_earner has been updated.
I've got the basic syntax for doing something when the column is updated but need a hand with the above to get this over the line.
ALTER TRIGGER [dsReplicated].[tr_mfeModified]
ON [dsReplicated].[matdb]
AFTER UPDATE
AS
BEGIN
IF (UPDATE(fee_earner))
BEGIN
print 'Matter fee earner changed to '
END
END
The problem with triggers in SQL server is that they are called one per SQL statement - not once per row. So if your UPDATE statement updates 10 rows, your trigger is called once, and the Inserted and Deleted pseudo tables inside the trigger each contain 10 rows of data.
In order to see if fee_earner has changed, I'd recommend using this approach instead of the UPDATE() function:
ALTER TRIGGER [dsReplicated].[tr_mfeModified]
ON [dsReplicated].[matdb]
AFTER UPDATE
AS
BEGIN
-- I'm just *speculating* here what you want to do with that information - adapt as needed!
INSERT INTO dbo.AuditTable (Id, TriggerTimeStamp, Mt_Code, Old_Fee_Earner, New_Fee_Earner)
SELECT
i.PrimaryKey, SYSDATETIME(), i.Mt_Code, d.fee_earner, i.fee_earner
FROM Inserted i
-- use the two pseudo tables to detect if the column "fee_earner" has
-- changed with the UPDATE operation
INNER JOIN Deleted d ON i.PrimaryKey = d.PrimaryKey
AND d.fee_earner <> i.fee_earner
END
The Deleted pseudo table contains the values before the UPDATE - so that's why I take the d.fee_earner as the value for the Old_Fee_Earner column in the audit table.
The Inserted pseudo table contains the values after the UPDATE - so that's why I take the other values from that Inserted pseudo-table to insert into the audit table.
Note that you really must have an unchangeable primary key in that table in order for this trigger to work. This is a recommended best practice for any data table in SQL Server anyway.
I have a database with two tables:
Table Student with the following
columns:
StudentID int identity,
StudentFN,
StudentLN,
Active bit,
EnrollmentDate
Table ArchivedStudent with the following columns:
ArvchivedStudentID int identity,
StudentID int,
StudentFN,
StudentLN,
WithdrawalDate getdate(),
ReasonDropped
In the long run, I'd like to schedule automatic updates for the table AcrchivedStudent and move the data from columns StudentID, StudentFN and StudentLN from table Student to table ArchnivedStudent when column Active changes from 1 (true) to 0 (false).
Here's my start up script that is not working:
update [as]
set [as].StudentID = s.StudentID,
[as].StudentFN = s.StudentFN,
[as].StudentLN = s.StudentLN
from ArchivedStudent [as]
inner join Student s
on [as].StudentID = s.StudentID
where s.Active = 0
go
The issue is that it does not return any results.
Once I'll be able to update table ArchivedStudent, I'd like to delete data of the students whose Active status changed to 0 in the Student table.
Your question still isn't very clear on the process. For example, do you want to allow the student to be deactivated for a certain period of time before they are moved to the archive table or do you want the student to be immediately moved to the archived table once the student is deactivated?
If the latter, this is much easier:
INSERT INTO ArchivedStudent (StudentId, StudentFn, StudentLn, WithdrawalDate)
SELECT S.StudentId, S.StudentFn, S.StudentLn, GETDATE()
FROM Student S
WHERE StudentId = ?
DELETE FROM Student WHERE StudentId = ?
If the former, then that is more challenging and we will require more detail.
Update 1:
To set the Withdrawal date based off a calculated value, use the following:
INSERT INTO ArchivedStudent (StudentId, StudentFn, StudentLn, WithdrawalDate)
SELECT S.StudentId, S.StudentFn, S.StudentLn, CAST(DATEADD(D,14,GETDATE()) AS DATE)
FROM Student S
WHERE StudentId = ?
Note 1: In DATEADD(), use a positive value for future dates and use a negative value for past dates. You can remove the DATE CAST if you need the actual time in addition to the date.
Note 2: The DELETE script posted in the original answer still stands.
You need a trigger to do it :
CREATE TRIGGER ArchiveStudent ON Student
FOR UPDATE
AS
BEGIN
SET NOCOUNT ON;
INSERT INTO ArchivedStudent (StudentID, StudentFN, StudentLN)
SELECT
StudentID
, StudentFN
, StudentLN
FROM
Student
WHERE
Active = 0
DELETE FROM Student
WHERE
Active = 0
END
However, your approach it's simple, and risky at the same time. For instance, if someone made a student inactive by mistake, then the trigger will immediately insert that student into archive table then deleted. Surely you can retrieve it by many ways such as deleted, inserted tables or even get the max id of archive table, but why you put yourself in this situation in the first place?. This is one of many general issues could be experienced by the current approach. A better approach is to actually add more versioning or historian methods for the tables, and make the archives run either from SQL Job or a store procedure on a fixed dates rather than triggers. this would give you a scheduled and controlled data archiving.
You can even add a historian columns which will store the value of active column and the date of the change. Then, use trigger or store procedure to do it for you (or even a computed column with a generic scalar function that will be reused on multiple tables). for instance, if the student is inactive for 5 business days, then archive it and delete it from the table.
You could use a TRIGGER AFTER UPDATE on the Student table.
This trigger would:
- react only on UPDATE,
- transfer Student to ArchiveStudent, when Active is set to 0
- and set WithdrawalDate to 2 weeks from today.
Trigger:
CREATE TRIGGER [Student_Changed]
ON Student
AFTER UPDATE
AS
BEGIN
-- Archive
INSERT INTO ArchiveStudent
(StudentID, StudentFN, StudentLN, WithdrawalDate)
SELECT
DELETED.StudentID
,DELETED.[StudentFN]
,DELETED.[StudentLN]
,DATEADD(day, 14, GETDATE()) -- 2 Weeks from today
FROM DELETED
WHERE DELETED.Active = 1
-- Delete archived
DELETE FROM Student
WHERE StudentID = (SELECT DELETED.[StudentID] FROM DELETED)
AND Active = 0
END;
DEMO:
You can take a look at the SQL Fiddle solution here.
There are a number of solutions here that all appear partially correct, but with some issues. Your initial update of your archive table will not insert into the archive table, only update an existing row. And since you are trying to join between the live table and the archive table, you will get no results - well, no updates since an update statement doesn't produce "results" as such anyway.
So as other have said you would use two statements - one an insert statement and one a delete. I would tend to be on the careful side and make sure that I a) dont get duplicates in my archive table and b) dont delete from live before I am sure its made it into the archive. So the two statements would be:
insert archivestudent(...fieldlist...)
select * from student
where active=0
and not exists(select * from archivestudent where archivestudent.studentid=student.studentid)
delete student
where active=0
and exists(select * from archivestudent where archivedstudent.studentid=student.studentid)
You can then run this code whenever you wish, schedule it as a job to run each night, whatever makes sense in your app.
If, on the other hand you want to immediately run then a trigger is the way to go. Be aware though that triggers are set-based operations, meaning that the trigger runs once for all rows affected by an update. This means that the solution proposed by #Milan will fail if the triggering update affects more than one row, because the clause WHERE StudentID = (SELECT DELETED.[StudentID] FROM DELETED) will return more one value. An example might be update student set active=0 where enrolmentdate<'2017-01-01'
You should always join to the internal tables exposed inside a trigger, in this case the DELETED table
delete student
from deleted
join student on student.studentid=deleted.studentid
where active=0
I'd still be tempted to add the where exists/not exists clauses inside the trigger as well just to make it more error-proof.
You need two queries:
Insert
Insert into archivedstudent (studentid, student, studentln) select studentid, studentfn, studentln from student where active=0 and studentid not in (select studentid from archivedstudent);
And the delete
Delete from student where studentid in (select studentid from archivedstudent);
What you need is a trigger.SQL Server Trigger After Update for a Specific Value However you should be careful with triggers on large amounts of data, they can hurt performance.
I have been searching for a way to log the deletion of rows from a table.
Tried this Log record changes in SQL server in an audit table but it didn't help me.
I have a song list database, the log table has the columns: Title / Artist / Year / Position / SentinDate .
There is a list with songs from the years 1999 to 2014, and every year has 2000 songs (top2000 is what it is called in The Netherlands).
Basically what the log table should look like once a certain Year has been deleted:
I need a basic way trigger-log when someone deletes a certain year from the list of 1999-2014.
I hope to have informed enough for you to understand, if not I will try to explain in more detail.
A trigger rejects or accepts each data modification transaction as a whole.
Using a correlated subquery in a trigger can force the trigger to examine the modified rows one by one.
Examples
A. Use an AFTER INSERT trigger
The following example assumes the existence of a table called newsale in the pubs database. This the CREATE statement for newsale:
CREATE TABLE newsale
(stor_id char(4),
ord_num varchar(20),
date datetime,
qty smallint,
payterms varchar(12),
title_id tid)
If you want to examine each of the records you are trying to insert, the trigger conditionalinsert analyzes the insert row by row, and then deletes the rows that do not have a title_id in titles.
CREATE TRIGGER conditionalinsert
ON sales
AFTER INSERT AS
IF
(SELECT COUNT(*) FROM titles, inserted
WHERE titles.title_id = inserted.title_id) <> ##ROWCOUNT
BEGIN
DELETE sales FROM sales, inserted
WHERE sales.title_id = inserted.title_id AND
inserted.title_id NOT IN
(SELECT title_id
FROM titles)
PRINT 'Only sales records with matching title_ids added.'
END
When unacceptable titles have been inserted, the transaction is not rolled back; instead, the trigger deletes the unwanted rows. This ability to delete rows that have been inserted relies on the order in which processing occurs when triggers are fired. First, rows are inserted into the sales table and the inserted table, and then the trigger fires.
Simply create an INSTEAD OF DELETE trigger ! In that trigger, you have a "virtual" table called deletedwhich contains all records which are to be deleted.
So in the trigger, you can just insert all records contained in deleted to your log table, and then you delete the records from our table. (this will then be a DELETE statement with a join to the deleted table)
Currently I have a Item table and a ItemWaste table.
Both tables will have some fields, such as: Name, Amount, etc. But the ItemWaste table will have one more field, which is the TimeWasted.
I wish to automatically insert the DELETED item from the Item table to the ItemWaste table, and at the same time insert the deletion time to the TimeWasted field.
I got no idea how to do this, is it using trigger???
Hope can get some help here... Appreciate any feedback... Thanks....
Sure - not a problem.
You need a basic AFTER DELETE trigger - something like this:
CREATE TRIGGER trg_ItemDelete
ON dbo.Item
AFTER DELETE
AS
INSERT INTO dbo.ItemWaste(Name, Amount, TimeWasted)
SELECT d.Name, d.Amount, GETDATE()
FROM Deleted d
That's all there is! One point to remember: the trigger is called once per batch - e.g. if you delete 100 rows at once, it will be called once and the pseudo table Deleted will contain 100 rows. The trigger is not called once per row (a common misconception).
Yes, simply by writting a trigger you can insert a row when an delete action is performed in another table, have a look at Triggers