+- 0Day Forums (https://zeroday.vip)
+-- Forum: Coding (https://zeroday.vip/Forum-Coding)
+--- Forum: Database (https://zeroday.vip/Forum-Database)
+--- Thread: How can I do a BEFORE UPDATED trigger with sql server? (/Thread-How-can-I-do-a-BEFORE-UPDATED-trigger-with-sql-server)
How can I do a BEFORE UPDATED trigger with sql server? - leathern789744 - 07-20-2023
I'm using Sqlserver express and I can't do `before updated` trigger. There's a other way to do that?
RE: How can I do a BEFORE UPDATED trigger with sql server? - blasto607 - 07-20-2023
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.
RE: How can I do a BEFORE UPDATED trigger with sql server? - unfaithfully616208 - 07-20-2023
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][1].
[1]:
[To see links please register here]
RE: How can I do a BEFORE UPDATED trigger with sql server? - prosiliently212090 - 07-20-2023
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.
RE: How can I do a BEFORE UPDATED trigger with sql server? - abbieabbot63 - 07-20-2023
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.
RE: How can I do a BEFORE UPDATED trigger with sql server? - lenders565821 - 07-20-2023
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...
>
>
[To see links please register here]
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:
[To see links please register here]
[tag:sql-server] [tag:triggers]
RE: How can I do a BEFORE UPDATED trigger with sql server? - frantic971 - 07-20-2023
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.
RE: How can I do a BEFORE UPDATED trigger with sql server? - demmer705 - 07-20-2023
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][1], 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.
[1]:
[To see links please register here]
RE: How can I do a BEFORE UPDATED trigger with sql server? - lobfig468382 - 07-20-2023
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
RE: How can I do a BEFORE UPDATED trigger with sql server? - elliotftrmxfah - 07-20-2023
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