I want to prevent further duplicates from being added to my table while allowing existing duplicates to remain. I thought I could accomplish this using a filtered index as follows.
But when I execute the following query:
CREATE UNIQUE INDEX IX_Account
ON Holdings(Account)
WHERE Account NOT IN (select Account from Holdings)
I get the following error:
Msg 1046, Level 15, State 1, Line 57
Subqueries are not allowed in this context. Only scalar expressions are allowed.
How can I prevent further duplicates from being added?
You can't have your cake and eat it.
Either
decide that your data should have integrity and purge the duplicated before adding the unique index (filtering it for the reason you mention does not make sense)
or
enforce your logic with an insert trigger:
create trigger no_more_duplicates on Holdings
after insert as
if exists
(
select 1
from inserted
where inserted.Account IN (select Account from Holdings)
)
raiserror('Cannot add duplicates',16,0)
end -- trigger
This trigger's a bit dumb, it will not prevent duplicates on a multiple-row insert, nor will it let the nonduplicate ones be saved. Yet, it's enough that you get the picture.
raiserror in a trigger will not automatically rollback the transaction, but throw will. Alternatively you can raiserror and rollback.
Also with an AFTER trigger the data in the INSERTED virtual table is already present in the table. So a trigger would need to look like:
use tempdb
drop table if exists Holdings
create table Holdings(id int primary key, Account int)
go
create or alter trigger no_more_duplicates on Holdings
after insert as
begin
if exists
(
select 1
from inserted
where inserted.Account IN (select Account from Holdings where id <> inserted.id)
)
begin
throw 60000, 'Cannot add duplicates', 1 ;
--raiserror('Cannot add duplicates',16,1)
end;
end -- trigger
go
insert into Holdings(id,Account) values (1,1)
go
insert into Holdings(id,Account) values (2,1)
go
select * from holdings
Related
I have create a triggers but its not working as I want. For example, I want to make sure that the order_limits filed should be between 1-10 and it should applied with insert and updates. But I cannot able to figure out how to make it work with updates and insert. Can anyone help me please?
Thanks
CREATE TRIGGER trRestrictRange
ON DATABASE
FOR ALTER_TABLE
AS
BEGIN
ALTER TABLE Order
ADD CONSTRAINT const_range CHECK (order_limits >=1 AND order_limits <= 10 );
END
If you "must" use a trigger (there is no good reason why you "must") then you need to use a DML trigger, not a DDL trigger, and check the data in the inserted pseudo table. Then, if the data exists in the table, THROW an error:
CREATE TRIGGER Chktrg_OrderRange ON dbo.YourTable
AFTER INSERT AS
BEGIN
IF EXISTS (SELECT 1
FROM inserted i
WHERE order_limits < 1
OR order_limits > 10)
THROW 98765, N'The Trigger check Chktrg_OrderRange on the table ''dbo.YourTable'' failed. The column ''order_limits'' must be more than or equal to one and less than or equal to 10.', 16;
END;
Of course, as I stated, there is no good reason to do this, and you should, instead, be using a CHECK CONSTRAINT:
ALTER TABLE dbo.YourTable ADD CONSTRAINT chk_OrderRange
CHECK (order_limits >= 1 AND order_limits <= 10);
I am trying to accomplish the following 3 simple tasks as a transaction (i.e. I need to lock old_table and new_table until the process completes).
Create a new table (new_table)
Add a trigger to old_table, which queues updates to new_table.
Select all the data from old_table and return it.
Note that I want these handled in a single transaction. I cannot allow inserts into old_table (and therefore triggered inserts into new_table) in between the trigger creation and the select on old_table.
My current closest attempt is this, but truthfully I feel that I am very far off from accomplishing my goal with this code. I have added the code just for reference of what I am trying, but I am mostly interested in non-specific answers that layout how to accomplish the above three comands in a transaction.
DROP PROCEDURE IF EXISTS dbo.BuildAll;
CREATE PROCEDURE dbo.BuildAll
AS
BEGIN
BEGIN TRANSACTION
DECLARE #TriggerCode VARCHAR(MAX)
CREATE TABLE dbo.new_table
(
status nvarchar(5),
type char(1),
col1 nvarchar(50),
col2 smallint
)
SELECT #TriggerCode = 'CREATE TRIGGER myTrigger
ON dbo.old_table FOR INSERT
AS
DECLARE #col1_new nvarchar(50)
DECLARE #col2_new smallint
SELECT #col1_new = col1 FROM inserted
SELECT #col2_new = col2 FROM inserted
IF #col1_new IS NOT NULL
BEGIN
INSERT INTO new_table (status, type, col1, col2)
SELECt "Q", "A", #col1, #col2 FROM inserted
END'
EXEC(#TriggerCode)
SELECT * FROM old_table
COMMIT
END
Going to suggest this an a possible solution you can try. This doesn't address the correctness of your actual trigger, you have two separate questions here really.
You don't need to encapsulate this entire process in a transaction.
Create your new table.
Create your trigger on old table, but disabled.
set transaction isolation level serializable
begin tran
go
create trigger <Name> on <Table> etc
go
disable trigger <Name> on <Table>
go
commit
Now in a transaction you can lock the old table against other activity while you work
begin tran
update oldtable with(tablockx) set column=column where id=0 /* block other processes from updating table, id=0 row doesn't exist */
query your data and process as required
enable trigger <Name> on <Table>
commit
This trigger code of yours is kinda odd .... you have a trigger on all three operations - yet it appears as if you're never using the values you fetch from the deleted pseudo table, and if the value from the inserted table is NULL, you're not doing anything inside your trigger - so you can really spare yourself the DELETE case - that'll never do anything....
Also, as mentioned in my comment - you Inserted pseudo table can easily contain multiple rows - but you're selecting from it as if you only ever expect it to contain a single row.
You should really rewrite your trigger code to handle the case of multiple rows in Inserted and make the whole thing properly set-based - something like this:
CREATE TRIGGER myTrigger
ON dbo.old_table
FOR INSERT, UPDATE
AS
INSERT INTO new_table (status, type, col1, col2)
SELECT 'Q', 'A', i.col1, i.col2
FROM Inserted i
Whether you need this on the UPDATE case at all - I cannot tell, you need to decide this. But basically: just select from the Inserted table, take the Col1 and Col2 values, and add the constant values 'Q' and 'A' to your insert to handle multiple rows properly. That should do it.
Recently, I needed to write a stored procedure to insert only one record when the first user come and ignore for others. I think the IF NOT EXISTS INSERT will not work for me. Also, some people saying online that MERGE adds race condition. Any quick way to achieve this? This is my code for now.
IF NOT EXISTS (SELECT ......)
INSERT
You might add another table to use as the lock mechanism.
Let's say your table's name is a, and the name of the table which has the locked value is check_a :
create table a (name varchar(10))
create table check_a (name varchar(10))
Insert only one record to the lock table:
insert into check_a values ('lock')
go
Then create a stored procedure which checks if there is a value in the main table. If there is no record, we might lock the only value in the table check_a and insert our value into the table a.
create proc insert_if_first
as
begin
set nocount on
if not exists (select name from a)
begin
declare #name varchar(10)
begin tran
select #name = name from check_a with (updlock)
if not exists (select name from a)
begin
insert into a values ('some value')
end
commit
end
end
go
First selection from the table a to check there is no record is for using system resources as low as we can. If there is a record in the table a, we can skip opening transaction and skip locking the row.
Second check is to make sure that while we are waiting to obtain the lock, no one inserted a row to the table a.
This way, only the first user which can lock check_a will be able to insert a value to the table a.
I'm guessing that you mean you want users to make a stored procedure that makes sure only one user can run the procedure. Then you need to use isolation levels. There are different Isolation levels, so you need to decide which one you need.
READ UNCOMMITTED
READ COMMITTED
REPEATABLE READ
SERIALIZABLE
You can read what they do here:
https://msdn.microsoft.com/en-us/library/ms173763.aspx
Im trying to make this trigger work when trying to delete a record. The way it is suposed to work is, when someone tries to delete a record it rollbacks and inserts an audit record to TbAudit table which by the way, all columns have a NOT NULL constraint. However, turns out it wont do it, because for some reason I dont understand when I try to delete a record it will display the message and rollback BUT all my variables within the select statement are getting NULL values even though Im pulling them directly from the "deleted" table. Please help.
USE BdPlan
GO
CREATE TRIGGER TrAudit
ON Plan.TPlan
AFTER DELETE
AS
BEGIN
DECLARE #IdPlan = int,
#IdEmployee int,
#Month int,
#Year int
ROLLBACK
PRINT 'CANT DELETE RECORDS'
-- All variables are getting NULL
SELECT #IdPlan = D.IdPlan,
#IdEmployee = D.IdEmployee ,
#Month = D.Month,
#Year = D.Year
FROM deleted AS D
INSERT INTO BdAudit.dbo.TbAudit
VALUES
(
#IdPlan,
#IdEmployee,
#Month,
#Year,
SUSER_NAME(),
GETDATE()
)
END
I believe there may be problems with this approach:
you are trying to access the DELETED pseudotable after the transaction has been rolled back - it will have zero rows after the rollback (see below)
your trigger only attempts to deal with a single row deletion - it should be able to handle multi row deletes
It is also noted that inserting directly into the Audit table from the Deleted pseudotable before ROLLBACK will of course roll the audit data back as well.
From here it is apparent you can cache the data to be audited in a #Temporary table variable, then do the ROLLBACK (which doesn't undo the #Temp table), and then do the Audit insertion:
ALTER trigger d_foo ON FOO AFTER DELETE
AS BEGIN
DECLARE #Temp AS TABLE
(
ID INT,
-- Obviously add all your fields go here
);
INSERT INTO #Temp(ID)
SELECT ID FROM DELETED;
ROLLBACK TRAN;
insert into fooaudit(id)
select id from #Temp;
END;
Simplified SqlFiddle here with multiple row deletion.
To confirm, the DELETED pseudotable contains zero rows after a ROLLBACK in a trigger, as this modified Fiddle demonstrates.
Is there anyway where I can create a trigger which will execute before the update/delete takes place( and then the actual update/delete takes place)? and how can I drop a trigger from a table?
to drop a trigger use:
--SQL Server 2005+, drop the trigger, no error message if it does not exist yet
BEGIN TRY DROP TRIGGER dbo.TrigerYourTable END TRY BEGIN CATCH END CATCH
GO
--drop trigger pre-SQl Server 2005, no error message if it does not exist yet
if exists (select * from sysobjects where id = object_id(N'[dbo].[TrigerYourTable ]') and OBJECTPROPERTY(id, N'IsTrigger') = 1)
drop trigger [dbo].[TrigerYourTable ]
GO
OP said in a comment:
...suppose I have to check childcount of
a perticular user if that is more than
5 do not update the user.how can I do
that using instead of trigger?
You don't really need to prevent the original update, you can let it happen, and then in the trigger check for the problem and rollback if necessary. This is how to enforce the logic for one or many affected rows, when you need to JOIN to determine the childcount of the affected rows:
--create the trigger
CREATE TRIGGER dbo.TrigerYourTable ON dbo.YourTable
AFTER UPDATE
AS
SET NOCOUNT ON
IF EXISTS (SELECT
1
FROM INSERTED i
INNER JOIN YourChildrenTable c ON i.ParentID=c.ParentID
GROUP BY i.ParentID
HAVING COUNT(i.ParentID)>5
)
BEGIN
RAISERROR('Count of children can not exceed 5',16,1)
ROLLBACK
RETURN
END
GO
It will throw the error if there is a violation of the logic, and the original command will be subject to a rollback.
If childcount is a column within the affected table, then use a trigger like this to enforce the logic:
--create the trigger
CREATE TRIGGER dbo.TrigerYourTable ON dbo.YourTable
AFTER UPDATE
AS
SET NOCOUNT ON
IF EXISTS (SELECT 1 FROM INSERTED WHERE childcount>5)
BEGIN
RAISERROR('Count of children can not exceed 5',16,1)
ROLLBACK
RETURN
END
GO
If you just want to ignore the update for any rows that violate the rule try this:
--create the trigger
CREATE TRIGGER dbo.TrigerYourTable ON dbo.YourTable
INSTEAD OF UPDATE
AS
SET NOCOUNT ON
UPDATE y
SET col1=i.col1
,col2=i.col2
,col3=i.col3
,.... --list all columns except the PK column!
FROM dbo.YourTable y
INNER JOIN INSERTED i on y.PK=i.PK
WHERE i.childcount<=5
GO
It will only update rows that have a child count less than 5, ignoring all affected rows that fail the requirement (no error message).
This article from microsoft explains the syntax of creating triggers.
http://msdn.microsoft.com/en-us/library/ms189799.aspx
There isn't really a 'before' trigger, but you can use an INSTEAD OF trigger that allows you to jump in place of whatever action is attempted, then define your own action.
I've used that technique for versioning data.
CREATE TRIGGER [dbo].[Documents_CreateVersion]
ON [dbo].[Documents]
INSTEAD OF UPDATE
AS
BEGIN
DECLARE #DocumentID int
SELECT DocumentID = DocumentID FROM INSERTED
-- do something
END
INSERTED is a bit of a misnomer here, but it contains the details of the action before it occurs you can then define your own action with that data.
Edit:
As per comments below my response, my example can be dangerous if multiple rows are updated at once. My application doesn't allow for this so it's fine in this case. I would agree that the above is a bad practice regardless.
to drop trigger- use database_name
IF EXISTS (SELECT name FROM sysobjects
WHERE name = 'tgr_name' AND type = 'TR')
DROP TRIGGER tgr_name
GO
Here's a simple trigger that checks columns values, and fires before updating or inserting, and raises an error.
IF OBJECT_ID ('dbo.MyTableTrigger', 'TR') IS NOT NULL
DROP TRIGGER dbo.MyTableTrigger;
GO
CREATE TRIGGER MyTableTrigger
ON dbo.MyTable
FOR INSERT, UPDATE
AS
DECLARE #Col1ID INT
DECLARE #Col2ID INT
SELECT #Col1ID = Col1ID, #Col2ID = Col2ID FROM inserted
IF ((#Col1ID IS NOT NULL) AND (#Col2ID IS NOT NULL))
BEGIN
RAISERROR ('Col1ID and Col2ID cannot both be in MyTable at the same time.', 16, 10);
END