I've discovered a new problem: I have a two tables, Classes and Students. Students references to Classes by [ClassID] column. Classes have column named [Count], which storing count of referencing students and I'm trying update it via AFTER INSERT,DELETE trigger on Students table.
I wrote a simple CALC_COUNT procedure like that:
CREATE PROCEDURE [dbo].[CALC_COUNT]
#classid INT
AS
BEGIN
UPDATE classes SET [Count] = (SELECT COUNT(Id) FROM students WHERE [ClassID] = #classid);
END
RETURN 0
and use it inside trigger
CREATE TRIGGER [MONITOR_STUDENTS_SCHEMA_TRIGGER]
ON [dbo].[students]
AFTER DELETE, INSERT
AS
BEGIN
UPDATE [dbo].[classes]
SET studentsschemarev +=1 FROM inserted;
CALC_COUNT(SELECT [ClassID] FROM inserted UNION SELECT [ClassID] FROM deleted);
UPDATE [dbo].[stats] SET students_schema_rev += 1;
END
But it not works.
I think, I need a way to execute procedure for each row in SELECT statement of trigger, but I don't know how.
SQL Server 2012 LocalDB, compatibility mode with SQL Server 2008.
You don't need your stored proc.
Update your trigger to be
update classes
set
count = StudentCount,
schemarevcount += 1
from
classes
inner join
(select * from inserted union select * from deleted) students
on classes.classid=students.classid
inner join
(select classid, count(*) as StudentCount from students group by classid) counts
on students.classid = counts.classid
in place of the update and the call to calc_count
An english translation...
Update classes (set the revision and the count)
where the class is changed in the students table
where that class is in the set of counts of students per class
Well, the main reason your trigger is not fired, is because you are doing an UPDATE where your trigger is going of on a INSERT and DELETE.
Yes, an UPDATE is a DELETE and INSERT, but you have to put it in your footprint :
AFTER DELETE, INSERT, UPDATE
instead of
AFTER DELETE, INSERT
Next, in the trigger itself you only have the internal conceptual tables called inserted and deleted, which combined give you the update. The old part is in the deleted table, the new part is in the inserted table.
Why you want to execute record by record by the way? Doing it with a complete resultset is much faster!
Related
i made a trigger which should avoid inserting a record in the rental 'uitlening' table if the person has an overdue payment (Boete). Unfortunately it doesnt work and i cant find the reason why. 'Boete' is an attribute of another table than rental. Can someone help me?
CREATE TRIGGER [dbo].[Trigger_uitlening]
ON [dbo].[Uitlening]
FOR INSERT
AS
BEGIN
DECLARE #Boete decimal(10, 2);
SET #Boete = (SELECT Boete FROM Lid WHERE LidNr = (SELECT LidNr FROM inserted));
IF #Boete = 0
BEGIN
INSERT INTO Uitlening
SELECT *
FROM inserted;
END;
END;
It sounds like what you actually need is a cross-table constraint.
You can either do this by throwing an error in the trigger:
CREATE TRIGGER [dbo].[Trigger_uitlening]
ON [Rental]
AFTER INSERT
AS
SET NOCOUNT ON;
IF EXISTS (SELECT 1
FROM inserted i
INNER JOIN dbo.Person p ON i.[personID] = p.[personID]
WHERE p.[PaymentDue] <= 0
)
THROW 50001, 'PaymentDue is less than 0', 1;
A better solution is to utilize a trick with an indexed view. This is based on an article by spaghettidba.
We first create a dummy table of two rows
CREATE TABLE dbo.DummyTwoRows (dummy bit not null);
INSERT DummyTwoRows (dummy) VALUES(0),(1);
Then we create the following view:
CREATE VIEW dbo.vwPaymentLessThanZero
WITH SCHEMBINDING -- needs schema-binding
AS
SELECT 1 AS DummyOne
FROM dbo.Rental r
JOIN dbo.Person p ON p.personID = r.personID
CROSS JOIN dbo.DummyTwoRows dtr
WHERE p.PaymentDue <= 0;
This view should in theory always have no rows in it. To enforce that, we create an index on it:
CREATE UNIQUE CLUSTERED INDEX CX_vwPaymentLessThanZero
ON dbo.vwPaymentLessThanZero (DummyOne);
Now if you try to add a row that qualifies for the view, it will fail with a unique violation, because the cross-join is doubling up the rows.
Note that in practice the view index takes up no space because there are never any rows in it.
Assuming you just want to insert records into [Rental] of those users, who have [PaymentDue] <= 0. As you mentioned in your last comment:
no record in rental can be inserted if the person has a PaymentDue
thats greater than zero
And other records should be silently discarded as you didn't give a clear answer to #Larnu's question:
should that row be silently discarded, or should an error be thrown?
If above assumptions are true, your trigger would look like:
CREATE TRIGGER [dbo].[Trigger_uitlening]
ON [Rental]
INSTEAD OF INSERT
AS
BEGIN
INSERT INTO [Rental] ( [DATE], [personID], [productID])
SELECT i.[DATE], i.[personID], i.[productID]
FROM INSERTED i
INNER JOIN Person p ON i.[personID] = p.[personID]
WHERE p.[PaymentDue] <= 0
END;
Attention! When you create a trigger by FOR INSERT or AFTER INSERT then don't write insert into table select * from inserted, because DB will insert data automatically, you can do only ROLLBACK this process. But, when creating a trigger by INSTEAD OF INSERT then you must write insert into table select * from inserted, else inserting not be doing.
I was just trying to figure out how to do a basic trigger when I updated a row
Heres the setup
CREATE TABLE marriage(
personid int
married varchar(20)
);
INSERT INTO marriage
values (1, unmarried);
What im trying to do is create a sql trigger that will make it so that when I update a person can only go from married to divorced but not unmarried to divorced.
If anyone can help me with structuring this that would be great
This is what I was looking for if someone was looking for something similar
alter trigger
trigtest3
on married
for update
as
begin
declare #old varchar(20)
declare #new varchar(20)
select #old = married from deleted
select #new = married from inserted
if(#old like 'Unmarried' AND #new like 'Divorced')
rollback
end
SQL Server doesn't provide per-row triggers unfortunately, but only triggers for a complete command. And one single update command can update several rows, so you must look whether at least one affected row has undergone a forbidden change. You do this by joining the deleted and inserted pseudo tables on a column or a combination of columns that uniquely identify a record (i.e. the primary key).
create trigger trg_upd_married on marriage for update as
begin
declare #error_count int
select #error_count = count(*)
from deleted d
join inserted i on i.id = d.id
where d.married = 'Unmarried'
where i.married = 'Divorced'
if #error_count > 0
begin
raiserror('Unmarried persons cannot get divorced.', 16, 121)
rollback transaction
end
end;
The above trigger may still have errors. I am not fluent with TSQL (and just notice that I find its triggers quite clumsy - at least compared to Oracle's triggers I am used to).
You need to use instead of triggers as you need to prevent update. For update triggers are run after the insert happens. Use the following code -
create trigger abc on marriage
for instead of update
as
begin
Begin transaction
if exists(select 1 from deleted as a
inner join inserted as b
on a.personid = b.personid
where a.married = 'unmarried' and b.married = 'Divorced')
begin
raiserror('Status can not be changed from unmarried to Divorced',16,1)
Rollback transaction
end
else
begin
update a
set a.married = b.married
from marriage as a
inner join inserted as b
on a.personid = b.personid
Commit transaction
end
end
Let me know if this helps
Much more complicated then this, but this is the basic
Person table (id, name, emailaddress)
Salesperson table (id, personID)
CustomerServiceRep table (id, personID)
Jeff is salesperson (id=4) and customerservicerep (id=5) with personID=1.
Simple
Trigger on SalesPerson Table
AFTER DELETE
AS
DECLARE #personID int = (SELECT personID FROM deleted);
IF #personID IS NOT NULL
BEGIN TRY
DELETE FROM Person
WHERE Person.id = #personID;
END TRY
BEGIN CATCH
END CATCH
DELETE FROM SalesPerson WHERE id=4;
Causes
Msg 3616, Level 16, State 1
An error was raised during trigger execution. The batch has been aborted and the user transaction, if any, has been rolled back.
I'm sure there's a much simpler way to not delete personID if it exists from some kind of constraint. Or catch the constraint. To go through every possible table that this could be in seems very repetitive and potentially more difficult when there are more tables/columns that may use this same table/constraint (foreign key).
You need an instead of delete trigger here rather than an after trigger.
CREATE Trigger tr_Delete_person
on Person
INSTEAD OF DELETE
AS
BEGIN
SET NOCOUNT ON;
-- Delete any child records
Delete FROM SalesPerson
WHERE EXISTS (SELECT 1 FROM deleted
WHERE personID = SalesPerson.personID)
Delete FROM CustomerServiceRep
WHERE EXISTS (SELECT 1 FROM deleted
WHERE personID = CustomerServiceRep .personID)
-- Finally delete from the person table
DELETE FROM Person
WHERE EXISTS (SELECT 1 FROM deleted
WHERE personID = Person .personID)
END
You also have a fundamental flaw in your trigger in that you seem to expect that the trigger will be fired once per row - this is NOT the case in SQL Server. Instead, the trigger fires once per statement, and the pseudo table Deleted might contain multiple rows.
Given that that table might contain multiple rows - which one do you expect will be selected here??
DECLARE #personID int = (SELECT personID FROM deleted);
It's undefined - you'll get the value from one, arbitrary row in Deleted, and all others are ignored - typically not what you want!
You need to rewrite your entire trigger with the knowledge the Deleted WILL contain multiple rows! You need to work with set-based operations - don't expect just a single row in Deleted !
I have an SQL Trigger FOR INSERT, UPDATE I created which basically does the following:
Gets a LineID (PrimaryID for the table) and RegionID From the Inserted table and stores this in INT variables.
It then does a check on joining tables to find what the RegionID should be and if the RegionID is not equal what it should be from the Inserted table, then it should update that record.
CREATE TRIGGER [dbo].[TestTrigger]
ON [dbo].[PurchaseOrderLine]
FOR INSERT, UPDATE
AS
-- Find RegionID and PurchaseOrderLineID
DECLARE #RegionID AS INT
DECLARE #PurchaseOrderLineID AS INT
SELECT #RegionID = RegionID, #PurchaseOrderLineID = PurchaseOrderLineID FROM Inserted
-- Find PurchaserRegionID (if any) for the Inserted Line
DECLARE #PurchaserRegionID AS INT
SELECT #PurchaserRegionID = PurchaserRegionID
FROM
(...
) UpdateRegionTable
WHERE UpdateRegionTable.PurchaseOrderLineID = #PurchaseOrderLineID
-- Check to see if the PurchaserRegionID has a value
IF #PurchaserRegionID IS NOT NULL
BEGIN
-- If PurchaserRegionID has a value, compare it with the current RegionID of the Inserted PurchaseOrderLine, and if not equal then update it
IF #PurchaserRegionID <> #RegionID
BEGIN
UPDATE PurchaseOrderLine
SET RegionID = #PurchaserRegionID
WHERE PurchaseOrderLineID = #PurchaseOrderLineID
END
END
The problem I have is that it is not updating the record and I'm guessing, it is because the record hasn't been inserted yet into the PurchaseOrderLine table and I'm doing an update on that. But can you update the row which will be inserted from the Inserted table?
The major problem with your trigger is that it's written in assumption that you always get only one row in INSERTED virtual table.
SQL Server triggers are statement-triggers not row-triggers. You have to take that fact into consideration.
Now if I understand correctly the logic behind this trigger then you need just one update statement in it
CREATE TRIGGER TestTrigger ON PurchaseOrderLine
FOR INSERT, UPDATE
AS
UPDATE l
SET RegionID = u.PurchaserRegionID
FROM PurchaseOrderLine l JOIN INSERTED i
ON l.PurchaseOrderLineID = i.PurchaseOrderLineID JOIN
(
SELECT PurchaseOrderLineID, PurchaserRegionID
FROM UpdateRegionTable -- !!! change this for your proper subquery
) u ON l.PurchaseOrderLineID = u.PurchaseOrderLineID
For this example I've created a fake table UpdateRegionTable. You have to change it to the proper query that returns PurchaseOrderLineID, PurchaserRegionID (in your code you replaced it with ...). Make sure that it returns all necessary rows, not one.
Here is SQLFiddle demo
I think the problem could be that you are making the update to PurchaceOrderLine inside the trigger that is monitoring updates to the same table as well. Try to alter the trigger to just monitor the inserts, than if this works, you can make some changes or break your trigger on two: one for inserts, another for updates.
This has been resolved. I resolved the problem by adding the trigger to another table as the IF #PurchaserRegionID IS NOT NULL was always false.
I have a table with multiple records:
User_Name ( e.g. 'TOM')
Question_ID (eg 'q002')
Answer (e.g. 'D')
i want to create a trigger so that no one can submit an answer to the same question twice.
It has to be a trigger only.
CREATE TRIGGER trigger_Check_Duplicates
ON submit_Answer
FOR INSERT
AS
IF SELECT???
PRINT 'duplicate'
raiserror('cant submit answer to same question twice')
ROLLBACK
End
Create trigger
CREATE TRIGGER dbo.uniqueUserQuestion
ON dbo.submit_Answer
INSTEAD OF INSERT
AS
BEGIN
SET NOCOUNT ON
IF EXISTS
(
SELECT 1
FROM dbo.submit_Answer T
INNER JOIN INSERTED I
ON T.user_name = I.user_name
AND T.question_id = I.question_id
)
BEGIN
-- Do dupe handling here
PRINT 'duplicate'
raiserror('cant submit answer to same question twice')
return
END
-- actually add it in
INSERT INTO
dbo.submit_Answer
SELECT
*
FROM
INSERTED I
END
GO
MySql does not support INSTEAD OF triggers, which is what you'd need to use here. In SQL Server, you'd use an INSTEAD OF INSERT trigger that will fire before the insert occurs, where you can write a check for the duplicate. However, if you can avoid a trigger, why not use a Stored Routine and just check for the duplicate before inserting?
This is, of course, if you really, really cannot use a constraint.
Edit: Updating answer for MSSQL.
Here's an example right from MSDN:
CREATE TRIGGER IO_Trig_INS_Employee ON Employee
INSTEAD OF INSERT
AS
BEGIN
SET NOCOUNT ON
-- Check for duplicate Person. If there is no duplicate, do an insert.
IF (NOT EXISTS (SELECT P.SSN
FROM Person P, inserted I
WHERE P.SSN = I.SSN))
INSERT INTO Person
SELECT SSN,Name,Address,Birthdate
FROM inserted
ELSE
-- Log an attempt to insert duplicate Person row in PersonDuplicates table.
INSERT INTO PersonDuplicates
SELECT SSN,Name,Address,Birthdate,SUSER_SNAME(),GETDATE()
FROM inserted
-- Check for duplicate Employee. If no there is duplicate, do an INSERT.
IF (NOT EXISTS (SELECT E.SSN
FROM EmployeeTable E, inserted
WHERE E.SSN = inserted.SSN))
INSERT INTO EmployeeTable
SELECT EmployeeID,SSN, Department, Salary
FROM inserted
ELSE
--If there is a duplicate, change to UPDATE so that there will not
--be a duplicate key violation error.
UPDATE EmployeeTable
SET EmployeeID = I.EmployeeID,
Department = I.Department,
Salary = I.Salary
FROM EmployeeTable E, inserted I
WHERE E.SSN = I.SSN
END
You'll obviously need to modify/simplify for your situation, but the basic context is there.