I have the following trigger, and I need that its only executed when one column value changes, is that possible?
ALTER TRIGGER [dbo].[TR_HISTORICO]
ON [dbo].[Tbl_Contactos]
AFTER UPDATE
AS
BEGIN
IF UPDATE (primerNombre) -- sólo si actualiza PRIMER NOMBRE
BEGIN
INSERT INTO [dbo].[Tbl_Historico] ([fecha],[idUsuario],[valorNuevo], [idContacto],[tipoHistorico] )
SELECT getdate(), 1, [dbo].[Encrypt]([dbo].[Decrypt](primerNombre)), [idContacto], 1
FROM INSERTED
END
END
The problem is the code is executed always even if another column changes
The problem is probably the way you are doing updates in your code. It may be updating every field and not only the one that changed.
In this case you need to check to see if there is a difference between the values in the inserted and deleted pseudo tables. Or fix your code so that it only updates what needs to be updated.
Comparing the value of primerNombre from the inserted and deleted tables
ALTER TRIGGER [dbo].[TR_HISTORICO] ON [dbo].[Tbl_Contactos]
AFTER UPDATE AS
BEGIN
INSERT INTO [dbo].[Tbl_Historico] ([fecha],[idUsuario],[valorNuevo], [idContacto],[tipoHistorico] )
SELECT getdate(), 1, [dbo].[Encrypt]([dbo].[Decrypt](i.primerNombre)), i.[idContacto], 1
FROM INSERTED i
inner join deleted d
on i.idContacto = d.idContacto
where i.primerNombre <> d.primerNombre
END
If primerNombre is nullable, the where will need to handle null comparisons as well.
Related
CREATE OR ALTER TRIGGER CheckQuantity
ON dbo.Products
AFTER UPDATE
AS
BEGIN
UPDATE dbo.Products
SET Product_ReOrder = 1
FROM Inserted i
WHERE i.Product_ID = dbo.Products.Product_ID
AND i.Product_QOH < 5;
I am not getting a syntax error
syntax error near ;
This is referring to the ; at the end of the code.
Not 100% sure what you're trying to do - you're not giving us much to go on, either!
I'm assuming you mean you want to set a column called Product_ReOrder in your table to 1 if another column Product_QOH is less than 5 - correct?
In that case - use a trigger something like this:
CREATE OR ALTER TRIGGER CheckQuantity
ON dbo.Products
AFTER UPDATE
AS
BEGIN
UPDATE dbo.Products
SET Product_ReOrder = 1
FROM Inserted i
WHERE i.PrimaryKeyColumn = dbo.Products.PrimaryKeyColumn
AND i.Product_QOH < 5;
END
The trigger will fire after an UPDATE, and Inserted will contain all rows (can and will be multiple rows!) that have been updated - so I'm assuming you want to check the quantity on those rows.
I'm joining the base table (dbo.Products) to the Inserted pseudo table on the primary key column of your table (which we don't know what it is - so you need to adapt this as needed), and I'm setting the Product_ReOrder column to 1, if the Products_QOH value is less than 5.
Your line of code
Select #QOH = (select Product_QOH from inserted)
has a fatal flaw of assuming that only one row was updated - this might be the case sometimes - but you cannot rely on that! Your trigger must be capable of handling multiple rows being updated - because the trigger is called only once, even if 10 rows are updated with a command - and then Inserted will contain all those 10 updated rows. Doing such a select is dangerous - you'll get one arbitrary row, and you'll ignore all the rest of them ....
Is that what you're looking for?
I'm unclear what you were thinking when you wrote this code, or what template you were basing off, but there are many syntax errors.
It seems you probably want something like this:
The update() function only tells us if that column was present in the update statement, not if anything was actually changed.
We need to check if we are being called recursively, in order to bail out.
We also check if no rows have been changed at all, and bail out early
Note how inserted and deleted are compared to see if any rows actually changed. This also deals correctly with multiple rows.
We then need to rejoin Products in order to update it.
create or alter trigger CheckQuantity
on Products
after update
as
set nocount on;
if not(update(Products_QOH))
or TRIGGER_NESTLEVEL(##PROCID, 'AFTER', 'DML') > 1
or not exists (select 1 from inserted)
return; -- early bail-out
update p
set Product_ReOrder = 1
from Products p
join (
select i.YourPrimaryKey, i.Products_QOH
from inserted i
where i.Product_QOH < 5
except
select d.YourPrimaryKey, d.Products_QOH
from deleted d
) i on i.YourPrimaryKey = p.YourPrimaryKey;
However, I don't understand why you are using a trigger at all.
I strongly suggest you use a computed column for this instead:
ALTER TABLE Products
DROP COLUMN Product_ReOrder;
ALTER TABLE Products
ADD Product_ReOrder AS (CASE WHEN Product_QOH < 5 THEN CAST(1 AS bit) ELSE CAST(0 AS bit) END);
Is it possible to make a column that can only be NULL from the beginning, but once it has been set to a non-null value then it can never be reset to NULL?
I'm guessing it might be possible with an update constraint using both the inserted and deleted table, but that seems somewhat complicated given the goal of the task.
Bonus question: Since it doesn't seem easy to do this, is this a sign of bad design (on the part of us / SQL Server)?
Since you're allowing the filed to be NULL when the ROW is Inserted, you'll have to use a Trigger for Update
CREATE TRIGGER trigger1 ON table1
FOR UPDATE
AS
BEGIN
SET NOCOUNT ON
DECLARE #field1 VARCAHR(MAX)
select #field1 = field1 FROM INSERTED
IF #field1 is NULL
BEGIN
RAISERROR('A NULL Values are not allowed', 15, 1)
ROLLBACK
END
END
"Allowing null value in a column initially, but once set to non null value, it must not allow null value for the same row"
This is clearly a business logic. It must be handled in controller part of MVC. Trying to handle it in database layer will break the MVC principle, and thus is a bad design.
If you still want to handle it in DBMS, then, as suggested in other answers, you can use triggers.
The trigger may look like this. You join INSERTED on DELETED to check if column was NOT NULL and became NULL:
CREATE TRIGGER trCheckForNulls ON SomeTable
AFTER UPDATE
AS
BEGIN
IF UPDATE(SomeColumn)
BEGIN
IF EXISTS(
SELECT * FROM INSERTED i
JOIN DELETED d ON i.PK = d.PK
WHERE d.SomeColumn IS NOT NULL AND i.SomeColumn IS NULL)
BEGIN
RAISERROR('SomeError', 16, 1)
ROLLBACK
END
END
END
How to create a trigger that updates a column in a table when a different column in the same table is updated.
So far I have done the following which works when any new data is created. Its able to copy data from "Purchase Requisition" to "PO_Number" however when data has been modified in "Purchase Requisition" , no changes is made to "PO_Number" and the value becomes NULL. Any kind help will be seriously appreciated.
ALTER TRIGGER [dbo].[PO_Number_Trigger]
ON [dbo].[TheCat2]
AFTER INSERT
AS BEGIN
UPDATE dbo.TheCat2 SET PO_Number=(select Purchase_Requisition from inserted) where DocNo= (Select DocNo from inserted);
END
You need to add 'UPDATE' as well as insert to the trigger, otherwise it will only execute on new data, not updated data. Also added 'top 1' to the select statements from the inserted table to allow this to be 'safe' on batch updates, however it will only update 1 record.
ALTER TRIGGER [dbo].[PO_Number_Trigger]
ON [dbo].[TheCat2]
AFTER INSERT, UPDATE
AS BEGIN
UPDATE dbo.TheCat2 SET PO_Number=(select top 1 Purchase_Requisition from inserted) where DocNo= (Select top 1 DocNo from inserted);
END
This might do what you want:
Your trigger is altering all rows in TheCat2. Presumably, you only want to alter the new ones:
ALTER TRIGGER [dbo].[PO_Number_Trigger]
ON [dbo].[TheCat2] AFTER INSERT
AS
BEGIN
UPDATE tc
SET PO_Number = Purchase_Requisition
FROM dbo.TheCat2 tc JOIN
inserted i
on tc.DocNo = i.DocNo ;
END;
However, perhaps a computed column is sufficient for your purposes:
alter table add PO_Number as Purchase_Requisition;
Question:
In our SQL-Server 2005 database, we have a table T_Groups.
T_Groups has, amongst other things, the fields ID (PK) and Name.
Now some idiot in our company used the name as key in a mapping table...
Which means now one may not alter a group name, because if one does, the mapping is gone...
Now, until this is resolved, I need to add a restriction to T_Groups, so one can't update the group's name.
Note that insert should still be possible, and an update that doesn't change the groupname should also be possible.
Also note that the user of the application & the developers have both dbo and sysadmin rights, so REVOKE/DENY won't work.
How can I do this with a trigger ?
CREATE TRIGGER dbo.yournametrigger ON T_Groups
FOR UPDATE
AS
BEGIN
IF UPDATE(name)
BEGIN
ROLLBACK
RAISERROR('Changes column name not allowed', 16, 1);
END
ELSE
BEGIN
--possible update that doesn't change the groupname
END
END
CREATE TRIGGER tg_name_me
ON tbl_name
INSTEAD OF UPDATE
AS
IF EXISTS (
SELECT *
FROM INSERTED I
JOIN DELETED D ON D.PK = I.PK AND ISNULL(D.name,I.name+'.') <> ISNULL(I.name,D.name+'.')
)
RAISERROR('Changes to the name in table tbl_name are NOT allowed', 16,1);
GO
Depending on your application framework for accessing the database, a cheaper way to check for changes is Alexander's answer. Some frameworks will generate SQL update statements that include all columns even if they have not changed, such as
UPDATE TBL
SET name = 'abc', -- unchanged
col2 = null, -- changed
... etc all columns
The UPDATE() function merely checks whether the column is present in the statement, not whether its value has changed. This particular statement will raise an error using UPDATE() but won't if tested using the more elaborate trigger as shown above.
This is an example of preserving some original values with an update trigger.
It works by setting the values for orig_author and orig_date to the values from the deleted pseudotable each time. It still performs the work and uses cycles.
CREATE TRIGGER [dbo].[tru_my_table] ON [dbo].[be_my_table]
AFTER UPDATE
AS
UPDATE [dbo].[be_my_table]
SET
orig_author = deleted.orig_author
orig_date = deleted.orig_date,
last_mod_by = SUSER_SNAME(),
last_mod_dt = getdate()
from deleted
WHERE deleted.my_table_id IN (SELECT DISTINCT my_table_id FROM Inserted)
ALTER TABLE [dbo].[be_my_table] ENABLE TRIGGER [tru_my_table]
GO
This example will lock any updates on SABENTIS_LOCATION.fk_sabentis_location through a trigger, and will output a detailed message indicating what objects are affected
ALTER TRIGGER dbo.SABENTIS_LOCATION_update_fk_sabentis_location ON SABENTIS_LOCATION
FOR UPDATE
AS
DECLARE #affected nvarchar(max)
SELECT #affected=STRING_AGG(convert(nvarchar(50), a.id), ', ')
FROM inserted a
JOIN deleted b ON a.id = b.id
WHERE a.fk_sabentis_location != b.fk_sabentis_location
IF #affected != ''
BEGIN
ROLLBACK TRAN
DECLARE #message nvarchar(max) = CONCAT('Update values on column fk_sabentis_location locked by custom trigger. Could not update entities: ', #affected);
RAISERROR(#message, 16, 1)
END
Some examples seem to be using:
IF UPDATE(name)
But this seems to evaluate to TRUE if the field is part of the update statement, even if the value itself has NOT CHANGED leading to false positives.
I have a table with a AutoIdentity column as its PK and a nvarchar column called "IdentificationCode". All I want is when inserting a new row, it will search the table for any preexisting IdentificationCode, and if any found roll back the transaction.
I have written the folowing trigger:
ALTER trigger [dbo].[Disallow_Duplicate_Ids]
on [dbo].[tbl1]
for insert
as
if ((select COUNT(*) from dbo.tbl1 e , inserted i where e.IdentificationNo = i.IdentificationNo ) > 0)
begin
RAISERROR('Multiple Ids detected',16,1)
ROLLBACK TRANSACTION
end
But when inserting new rows, it always triggers the rollback even if there is no such IdentificationCode.
Can any one help me please?
thanks
As #Qpirate mentions, you should probably put some sort of UNIQUE constraint on the column. This is probably 'stronger' than using a trigger, as there's ways to disable those.
Also, the implicit-join syntax (comma-separated FROM clause) is considered an SQL anti-pattern - if possible, please always explicitly declare your joins.
I suspect that your error is because your trigger seems to be an AFTER trigger, and you check to see if there are any (non-zero) rows in the table; in other words, the trigger is (possibly) 'failing' the INSERT because it was INSERTed. Changing it to a BEFORE (or INSTEAD OF) trigger, or changing the count to >= 2 may solve the problem.
Without seeing your insert statement, it's impossible to know for sure, but (especially if you're using a SP), you may be able to check for existence in the INSERT statement itself, and throw an error (or do something else) if the row isn't inserted.
For example, the following:
INSERT INTO tbl1 (identificationCode, *otherColumns*)
VALUES (#identificationCode, *otherColumns)
WHERE NOT EXISTS (SELECT '1'
FROM tbl1
WHERE identificationCode = #identificationCode)
Will return a code indicating 'row not found' (inserted, etc; on pretty much every system this is SQLCODE = 100) if identificationCode is already present.
Use EXISTS to check if the IdentificationCode already exist.
If EXISTS (Select * from tbl1 where IdentificationCode = #IdentificationCode )
BEGIN
//do something
END
Else
BEGIN
//do something
END