I need a SQL trigger that would zero pad a cell whenever its inserted or updated. Was curious if its best practice to append two strings together like I'm doing in the update command. Is this be best way to do it?
CREATE TRIGGER PadColumnTenCharsInserted ON Table
AFTER INSERT
AS
DECLARE
#pad_characters VARCHAR(10),
#target_column NVARCHAR(255)
SET #pad_characters = '0000000000'
SET #target_column = 'IndexField1'
IF UPDATE(IndexField1)
BEGIN
UPDATE Table
SET IndexField1 = RIGHT(#pad_characters + IndexField1, 10)
END
GO
Your padding code looks fine.
Instead of updating every row in the table like this:
UPDATE Table
update just the row that triggered the trigger:
UPDATE updated
Also, you've still got some extraneous code -- everything involving #target_column. And it looks like you're not sure if this is an INSERT trigger or an UPDATE trigger. I see AFTER INSERT and IF UPDATE.
Two questions:
What are you doing with #target_column? You declare it and set it with a column name, but then you never use it. If you intend to use the variable in your subsequent SQL statements, you may need to wrap the statements in an EXECUTE() or use sp_executesql().
The syntax "UPDATE Table..." is OK for your update statement assuming that "Table" is the name of the table you are updating. What seems to be missing is a filter of some kind. Or did you really intend for that column to be updated for every row in the whole table?
One way to handle this would be to declare another variable and set it with the PK of the row that is updated, then use a where clause to limit the update to just that row. Something like this:
DECLARE #id int
SELECT #id = Record_ID FROM INSERTED
-- body of your trigger here
WHERE Record_ID = #id
I like your padding code. It looks good to me.
Related
I have a Products table with columns QtySold_Day and QtySold_Yesterday, which contain information about the quantity of sold products today and yesterday respectively.
I want to create a trigger that moves every single value from the QtySold_Day column to the QtySold_Yesterday whenever there's an attempt to update the QtySold_Day column.
This is what I already have:
create or alter trigger UpdateQuantity
on Products
instead of update
as
declare #x int
set nocount on
while (#x < ##ROWCOUNT)
begin
update Products
set QtySold_Day = QtySold_Yesterday
where (ProductID = #x)
end
I'd like to know how can I finish the trigger for it to work as intended.
SQL is a set based language, so you should always attempt set based operations. Inside a trigger you have access to a pseudo table called Inserted which has the new details of the update. You can therefore update all the relevant records in one go.
As commented you are probably going to need a way to avoid copying the values over if the record is updated multiple times - so I have added a check to ensure it only happens once. That might not be quite the behaviour you want so if you clarify we can tweak it.
Do you really want an INSTEAD OF trigger? Because that will capture ALL updates to this table, and for the most part do nothing.
UPDATE Products SET
QtySold_Day = QtySold_Yesterday
WHERE ProductID IN (SELECT ID FROM Inserted)
-- Only update once
AND QtySold_Yesterday IS NULL;
I'm going to create a trigger for update. Purpose of this trigger is that If muadurum column is changed , take the old value of mua_tarih in table fkayitlar and insert to another table mua_tarihleri.
My code block like;
ALTER TRIGGER [dbo].[trgr_fkayit_update]
ON [dbo].[fkayitlar]
AFTER UPDATE
AS
DECLARE #mua_durum_once NVARCHAR(10)
DECLARE #mua_durum_sonra NVARCHAR(10)
DECLARE #mua_tarih_once DATE
DECLARE #mua_yapan_once NVARCHAR(25)
DECLARE #kisi_id INT
Take the old value;
SELECT
#kisi_id=kayitid,
#mua_durum_once=muayenedurum,
#mua_tarih_once=muayenetarih,
#mua_yapan_once=mua_yapan
FROM deleted
Take the new value;
SELECT #mua_durum_sonra=muayenedurum FROM inserted
Check if value is changed ; if changed, Insert #mua_tarih to table mua_tarihleri with #kisi_id and #mua_yapan_once
IF #mua_durum_once='OLDU'
AND #mua_durum_sonra='OLMADI'
AND #mua_tarih_once IS NOT NULL
BEGIN
INSERT INTO mua_tarihleri(kayitid,mua_tarihi,mua_yapan)
VALUES(#kisi_id,#mua_tarih_once,#mua_yapan_once)
END
My problem is When I update more than one row in table fkayitlar,Trigger is working, but I see only one inserted row in table mua_tarihleri (only working once). I need to see more than one.(should be working more than once) Are not Triggers working on more than one process? or How can I solve this my problem?
The trigger only occurs once when the table is updated, no matter how many rows are updated. Therefore, you have to write your trigger body to operate on a set of rows, not a single row as you have done.
Should be something like:
ALTER TRIGGER [dbo].[trgr_fkayit_update]
ON [dbo].[fkayitlar]
AFTER UPDATE
AS
INSERT INTO mua_tarihleri(kayitid,mua_tarihi,mua_yapan)
SELECT deleted.kayitid, deleted.muayenedurum, deleted.muayenetarih, deleted.mua_yapan
FROM deleted
JOIN inserted ON deleted.kayitid = inserted.kayitid
WHERE deleted.muayenedurum='OLDU'
AND inserted.muayenedurum='OLMADI'
AND muayenetarih IS NOT NULL
I have a database that needs from time to time an update.
It may also happens that there are new data while the update runs.
In MySQL there is a option
INSERT INTO IGNORE
I can't find something like this in T-SQL.
No Problem to update ID 1-4 but then there is a new record for ID 5.
The UPDATE query don't work here.
And when I try to INSERT all data again I get a DUPLICATE KEY error.
Additional Infos:
I've forgotten to say that my data come from external sources. I call an API to get data from it. From there I have to insert these data into my database.
I have to admit that I don't understand MERGE. So my solution for now is to use TRUNCATE first and then insert all data again.
Not the best solution but MERGE works, so far I understand it, with two tables. But I have only one table. And to create a table temporarly to use MERGE and later drop that table is in my eyes a bit to much for my little table with 200 records in it.
You can use MERGE keyword. Basically, you need to specify the column(s) on which to join the source of data with target table, and depending on whether it is matching (existing record) or not matching (new record), you run an UPDATE or INSERT.
Reference: http://msdn.microsoft.com/en-us/library/bb510625.aspx
Is a stored procedure an option?
CREATE PROCEDURE dbo.Testing (#ID int, #Field1 varchar(20))
AS
BEGIN
UPDATE tblTesting
SET Field1 = #Field1
WHERE ID = #ID
IF ##ROWCOUNT = 0
INSERT INTO tblTesting (ID, Field1) SELECT #ID, #Field1
END
I need to decrease a counter in a table schedules, when there was an insert in enrollments table:
CREATE TRIGGER [UpdateEnrollmentsTrigger]
ON [TBLENROLLMENT_ENR]
FOR INSERT
AS
BEGIN
DECLARE #ScheduleCode NVARCHAR
DECLARE #TotalSlots INT
IF EXISTS(SELECT SCH_CODE FROM inserted)
BEGIN
SELECT #ScheduleCode = SCH_CODE FROM inserted
SELECT #TotalSlots = SCH_TOTALSLOTS FROM TBLSCHEDULES_SCH
WHERE SCH_CODE = #ScheduleCode
UPDATE TBLSCHEDULES_SCH
SET SCH_FREESLOTS = #TotalSlots - 1
WHERE SCH_CODE = #ScheduleCode
END
END
When I trying to create this trigger, the query window of VS12 says:
SQL46010 :: Incorrect syntax near ].
Thanks in advance.
The specific error is because you are using FOR INSERT instead of AFTER INSERT, but there are other things that you should improve on your trigger.
First of all, always, always write the length of a NVARCHAR, leaving it blank will behave differently depending where it's used. So replace DECLARE #ScheduleCode NVARCHAR with DECLARE #ScheduleCode NVARCHAR(n), where n is the required length.
I'm also not sure why you are doing the IF EXISTS since it's reading the INSERTED pseudo table, that it's bound to have records because the trigger was fired.
Another thing to improve is that you are assuming that only one row was inserted, as you are storing it on a variable, that's wrong and it will behave incorrectly if you insert more than just one row.
Oh, I almost forgot, you should also always specify the schema, for instance: CREATE TRIGGER [UpdateEnrollmentsTrigger] ON [TBLENROLLMENT_ENR] should be CREATE TRIGGER dbo.[UpdateEnrollmentsTrigger] ON dbo.[TBLENROLLMENT_ENR] (using the correct schema, of course)
I'm using Sqlserver express and I can't do before updated trigger. There's a other way to do that?
MSSQL does not support BEFORE triggers. The closest you have is INSTEAD OF triggers but their behavior is different to that of BEFORE triggers in MySQL.
You can learn more about them here, and note that INSTEAD OF triggers "Specifies that the trigger is executed instead of the triggering SQL statement, thus overriding the actions of the triggering statements." Thus, actions on the update may not take place if the trigger is not properly written/handled. Cascading actions are also affected.
You may instead want to use a different approach to what you are trying to achieve.
It is true that there aren't "before triggers" in MSSQL. However, you could still track the changes that were made on the table, by using the "inserted" and "deleted" tables together. When an update causes the trigger to fire, the "inserted" table stores the new values and the "deleted" table stores the old values. Once having this info, you could relatively easy simulate the "before trigger" behaviour.
Can't be sure if this applied to SQL Server Express, but you can still access the "before" data even if your trigger is happening AFTER the update. You need to read the data from either the deleted or inserted table that is created on the fly when the table is changed. This is essentially what #Stamen says, but I still needed to explore further to understand that (helpful!) answer.
The deleted table stores copies of the affected rows during DELETE and
UPDATE statements. During the execution of a DELETE or UPDATE
statement, rows are deleted from the trigger table and transferred to
the deleted table...
The inserted table stores copies of the affected rows during INSERT
and UPDATE statements. During an insert or update transaction, new
rows are added to both the inserted table and the trigger table...
https://msdn.microsoft.com/en-us/library/ms191300.aspx
So you can create your trigger to read data from one of those tables, e.g.
CREATE TRIGGER <TriggerName> ON <TableName>
AFTER UPDATE
AS
BEGIN
INSERT INTO <HistoryTable> ( <columns...>, DateChanged )
SELECT <columns...>, getdate()
FROM deleted;
END;
My example is based on the one here:
http://www.seemoredata.com/en/showthread.php?134-Example-of-BEFORE-UPDATE-trigger-in-Sql-Server-good-for-Type-2-dimension-table-updates
sql-server triggers
T-SQL supports only AFTER and INSTEAD OF triggers, it does not feature a BEFORE trigger, as found in some other RDBMSs.
I believe you will want to use an INSTEAD OF trigger.
All "normal" triggers in SQL Server are "AFTER ..." triggers. There are no "BEFORE ..." triggers.
To do something before an update, check out INSTEAD OF UPDATE Triggers.
To do a BEFORE UPDATE in SQL Server I use a trick. I do a false update of the record (UPDATE Table SET Field = Field), in such way I get the previous image of the record.
Remember that when you use an instead trigger, it will not commit the insert unless you specifically tell it to in the trigger. Instead of really means do this instead of what you normally do, so none of the normal insert actions would happen.
Full example:
CREATE TRIGGER [dbo].[trig_020_Original_010_010_Gamechanger]
ON [dbo].[T_Original]
AFTER UPDATE
AS
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;
DECLARE #Old_Gamechanger int;
DECLARE #New_Gamechanger int;
-- Insert statements for trigger here
SELECT #Old_Gamechanger = Gamechanger from DELETED;
SELECT #New_Gamechanger = Gamechanger from INSERTED;
IF #Old_Gamechanger != #New_Gamechanger
BEGIN
INSERT INTO [dbo].T_History(ChangeDate, Reason, Callcenter_ID, Old_Gamechanger, New_Gamechanger)
SELECT GETDATE(), 'Time for a change', Callcenter_ID, #Old_Gamechanger, #New_Gamechanger
FROM deleted
;
END
END
The updated or deleted values are stored in DELETED. we can get it by the below method in trigger
Full example,
CREATE TRIGGER PRODUCT_UPDATE ON PRODUCTS
FOR UPDATE
AS
BEGIN
DECLARE #PRODUCT_NAME_OLD VARCHAR(100)
DECLARE #PRODUCT_NAME_NEW VARCHAR(100)
SELECT #PRODUCT_NAME_OLD = product_name from DELETED
SELECT #PRODUCT_NAME_NEW = product_name from INSERTED
END