There is the table OLD and a similar one, NEW. I want to insert in the existing process that fills the table OLD a trigger event that for each new inserted row, this event will insert the newly inserted row to table NEW, as well. Inside the body of trigger, i need to include the query BELOW which aggregates values of OLD before inserted in NEW:
insert into NEW
select (select a.id,a.name,a.address,b.jitter,a.packet,a.compo,b.rtd,a.dur from OLD a,
select address,packet,compo, avg(jitter) as jitter, avg(rtd) as rtd from OLD
group by address,packet,compo ) b
where a.address=b.address and a.packet=b.packet and a.compo=b.compo;
can you correct any possible mistakes or suggest other trigger syntax on the statement below?
CREATE OR REPLACE TRIGGER insertion
after update on OLD
for each row
begin
MY select query above
end;
In a for each row trigger you cannot query the table itself. You will get a mutating table error message if you do.
I recommend only to use triggers for the most basic functionality such as handing out ID numbers and very basic checks.
If you do use triggers for more complex tasks you may very easily end up with a system that's very hard to debug and maintain because of all kinds of actions that appear out of knowhere.
Look at this question for another approach: getting rid of Insert trigger
Oracle Streams might also be a good solution. In the apply handler, you can include your own custom PL/SQL code. This procedure will be called after the COMMIT, so you can avoid mutating table errors.
However, Streams requires a large amount of setup to make it work. It might be overkill for what you are doing.
Related
For my homework I need to make a package that contains a procedure that removes all records from the table dwdimartist and then fills the table with all records from the table artist and add a field with the date of today.
This is what I've created, it works but I don't know if it's performant enough. Is it better to use a cursor that loops over each record in the table artist?
CREATE OR REPLACE PACKAGE BODY dwh AS
PROCEDURE filldwh IS
today_date DATE := SYSDATE;
BEGIN
DELETE FROM dwdimartist;
INSERT INTO dwdimartist (artistkey, name) (SELECT artistid, name FROM artist);
UPDATE dwdimartist SET added = today_date;
END filldwh;
END dwh;
Simple SQL query like you did is better choice than a cursor or implicit loop.
possible improvement:
You should do it at once without update: set the date during insert.
INSERT INTO dwdimartist (artistkey, name, added)
(SELECT artistid, name, sysdate FROM artist);
Hope it helps
You don’t need to use cursors. You can hardly beat Insert ... select since it’s SQL itself and in most cases it works better than any programmatic structure due to native dbms optimization. However, you can do better if you decrease number of I/O operations. You don’t need update here. Simply add sysdate to your select and insert everything together.
insert into dwdimartist(artistkey, name, added) select artistid, name, sysdate from artist;
Another thing to improve is your ‘delete’. While it’s small table for learning purposes you won’t feel any difference between delete and truncate but for real ETL tasks and big tables you’ll see it definitely. Yes you cannot use truncate directly in your PL/SQL but there are 3 ways to do it:
execute immediate ‘truncate dwdimartist’;
Dbms_utility.exec_ddl_statement(‘truncate ...;’);
DBMS_SQL package
However, remember that calling truncate will execute commit like any ddl command. So delete may be the only option sometimes. But even if it is, you should avoid it for the whole table.
I refactored a table that stored both metadata and data into two tables, one for metadata and one for data. This allows metadata to be queried efficiently.
I also created an updatable view with the original table's columns, using sqlite's insert, update and delete triggers. This allows calling code that needs both data and metadata to remain unchanged.
The insert and update triggers write each incoming row as two rows - one in the metadata table and one in the data table, like this:
// View
CREATE VIEW IF NOT EXISTS Item as select n.Id, n.Title, n.Author, c.Content
FROM ItemMetadata n, ItemData c where n.id = c.Id
// Trigger
CREATE TRIGGER IF NOT EXISTS item_update
INSTEAD OF UPDATE OF id, Title, Author, Content ON Item
BEGIN
UPDATE ItemMetadata
SET Title=NEW.Title, Author=NEW.Author
WHERE Id=old.Id;
UPDATE ItemData SET Content=NEW.Content
WHERE Id=old.Id;
END;
Questions:
Are the updates to the ItemMetadata and ItemData tables atomic? Is there a chance that a reader can see the result of the first update before the second update has completed?
Originally I had the WHERE clauses be WHERE rowid=old.rowid but that seemed to cause random problems so I changed them to WHERE Id=old.Id. The original version was based on tutorial code I found. But after thinking about it I wonder how sqlite even comes up with an old rowid - after all, this is a view across multiple tables. What rowid does sqlite pass to an update trigger, and is the WHERE clause the way I first coded it problematic?
The documentation says:
No changes can be made to the database except within a transaction. Any command that changes the database (basically, any SQL command other than SELECT) will automatically start a transaction if one is not already in effect.
Commands in a trigger are considered part of the command that triggered the trigger.
So all commands in a trigger are part of a transaction, and atomic.
Views do not have a (usable) rowid.
Suppose there are n number of tables in the database. Whatever insert,update,delete happen across any table in the database, have to be captured in a table called "Audit_Trail", where we have the below columns in the audit trail tables.
Server_Name
AT_date
AT_time
Table_name
Column_name
Action
Old_value
New_Value
The server on which table, on which column, on which date and time need to be captured. Also, the "Action" column tracks whether an action is an insert, update or delete and we have to capture the old value and new value as well.
So what is the best way to do this? Can we create a database level trigger which can fire trigger in case of any insert, update or delete?
The best way would be to use Oracle's own auditing functionality.
AUDIT ALL ON DEFAULT BY ACCESS;
http://docs.oracle.com/cd/E11882_01/network.112/e36292/auditing.htm#DBSEG392
In response to comment ...
There is nothing unusual in wanting to audit every change made to tables in the database -- hence there is already functionality provided in the system for doing exactly that. It is better then using triggers because it cannot be bypassed as easily. However, if you want to use this pre-supplied, robust, simple to use functionality you might have to compromise on your specific requirements a little, but the payoff will be a superior solution that will use code and configuration in common with thousands of other Oracle systems.
I'm unable to retrieve the latest inserted id from my SQL Server 2000 db using a typed dataset in asp.NET
I have created a tableadapter and I ticked the "Refresh datatable" and "Generate Insert, Update and Delete statements". This auto-generates the Fill and GetData methods, and the Insert, Update, Select and Delete statements.
I have tried every possible solution in this thread
http://forums.asp.net/t/990365.aspx
but I'm still unsuccesfull, it always returns 1(=number of affected rows).
I do not want to create a seperate insert method as the auto-generated insertCommand perfectly suits my needs.
As suggested in the thread above, I have tried to update the InsertCommand SQL syntax to add SELECT SCOPY_IDENTITY() or something similar, I have tried to add a parameter of type ReturnValue, but all I get is the number of affected rows.
Does anyone has a different take on this?
Thanks in advance!
Stijn
I decided to give up, I can't afford to waste any more time on this.
I use the Insert statement after which I do a select MAX(id) query to hget the insert ID
If anyone should have a solution, I'll be glad to read it here
Thanks
Stijn
I successfully found a way to get the incremental id after insert using my table adapter.
My approach is a little different, I'm using a Store procedure to make the insert, so my insert command has all the values but the ID, I made the sp return the ID just calling:
SET #ID=SCOPE_IDENTITY()
and then
COMMIT TRAN
and last line will be
RETURN #ID
Then I searched my table adapter parameters for InsertCommand and set the #RETURNVALUE to the column of the incremental ID of the table, so when it's executed automatically put the return value on the id field.
Hope this help
You need to tell your table's table-adapter to refresh the
data-table after update/insert operation.
This is how you can do that.
Open the properties of TableAdapter -> Default Select Query -> Advnaced options. and Check the option of Refresh the data table. Save the adapter now. Now when you call update on table-adapter, the data-table will be updated [refreshed] after the update/insert operation and will reflect the latest values from database table. if the primary-key or any coloumn is set to auto-increment, the data-table will have those latest value post recent update.
Now you can Call the update as TableAdapterObj.Update(ds.dataTable);
Read latest values from the DataTable(ds.dataTable) coloumns and assign respective values into the child table before update/insert. This will work exactly the way you want.
alt text http://ruchitsurati.net/files/tds1.png
I will explain problem with an example:
There is two table in my database, named entry, tags
There is a column named ID_ENTRY in both table. When I add a record to table, entry, I have to take the ID_ENTRY of last added record and add it to table, tags. How can I do it?
The only way to do this is with multiple statements. Using dynamic sql you can do this by separating each statement in your query string with a semi-colon:
"DECLARE #ID int;INSERT INTO [Entry] (...) VALUES ...; SELECT #ID = scope_identity();INSERT INTO [TAGS] (ID_ENTRY) VALUES (#ID);"
Make sure you put this in a transaction to protect against concurrency problems and keep it all atomic. You could also break that up into two separate queries to return the new ID value in the middle if you want; just make sure both queries are in the same transaction.
Also: you are using parameterized queries with your dynamic sql, right? If you're not, I'll personally come over there and smack you 10,000 times with a wet noodle until you repent of your insecure ways.
Immediatly after executing the insert statement on first table, you should query ##IDENTITY doing "SELECT ##identity". That will retrieve the last autogenerated ID... and then just insert it on the second table.
If you are using triggers or something that inserts rows... this may be not work. Use Scope_Identity() instead of ##IDENTITY
I would probably do this with an INSERT trigger on the named entry table, if you have all of the data you need to push to the tags table available. If not, then you might want to consider using a stored procedure that creates both inside a transaction.
If you want to do it in code, you'll need to be more specific about how you are managing your data. Are you using DataAdapter, DataTables, LINQ, NHibernate, ...? Essentially, you need to wrap both inserts inside a transaction of some sort so that either inserts get executed or neither do, but the means to doing that depend on what technology you are using to interact with the database.
If you use dynamic sql, why not use Linq to Entity Framework, now EF is the recommend data access technology from Microsoft (see this post Clarifying the message on L2S Futures from ADO.NET team blog), and if you do an insert with EF the last identity id will available for you automatically, I use it all the time it's easy.
Hope this helps!
Ray.