I am seeking suggestions on methods to trigger the running of code based on specific event occurring.
Basically I need to monitor all inserts into a table and compare a column value against a parameter set in another table.
For example, when a new record is added to the table and the column [Temperature] is greater than 30 (which is a value set in another table). Send an alert email to notify of this situation.
You can create a trigger (special type of stored procedure) that is automatically executed after an insert happened. Documentation for triggers is here: https://technet.microsoft.com/en-us/library/ms189799(v=sql.120).aspx
You will not be able to send an email out of SQL Database though.
Depending on how quick you need the notification after the insert, maybe you could make an insert into yet another table from within the trigger and query this new table periodically (e.g. using a script in Azure automation) and have the email logic outside the database.
Related
We have this pair of trigger and function that we use on our psql database for the longest time. Basically, the trigger is called each time there is a new record to the main table, and each row is inserted to the monthly partition individually. Following is the trigger function:
CREATE TRIGGER partition_mic_teams_endpoint_trg1
BEFORE INSERT ON "mic_teams_endpoint"
FOR EACH ROW EXECUTE
PROCEDURE trg_partition_mic_teams_endpoint('month');
The function we have creates monthly partitions based on a timestamp field in each row.
I have two questions:
List item Even if I try to COPY a bunch of rows from CSV to the main table, is this trigger/function going to insert each row individually? Is this efficient?
If that is the case, is it possible to have support for COPYing data to partitions instead of INSERT.
Thanks,
Note: I am sorry if I did not provide enough information for an answer
Yes, a row level trigger will be called for each row separately, and that will make COPY quite a bit slower.
One thing you could try is a statement level AFTER trigger that uses a transition table, so that you can
INSERT INTO destination SELECT ... FROM transition_table;
That should be faster, but you should test it to be certain.
See the documentation for details.
In some database project, I have a users table which somehow has a computed value avg_service_rating. And there is another table called services with all the services associated to the user and the ratings for that service. Is there a computationally-lite way which I can maintain the avg_service_rating rating without updating it every time an INSERT is done on the services table? Perhaps like a generate column but with a function call instead? Any direct advice or link to resources will be greatly appreciated as well!
CREATE TABLE users (
username VARCHAR PRIMARY KEY,
avg_service_ratings NUMERIC -- is it possible to store some function call for this column?,
...
);
CREATE TABLE service (
username VARCHAR NOT NULL REFERENCE users (username);
service_date DATE NOT NULL,
rating INTEGER,
PRIMARY KEY (username, service_date),
);
If the values should be consistent, a generated column won't fit the bill, since it is only recomputed if the row itself is modified.
I see two solutions:
have a trigger on the services table that updates the users table whenever a rating is added or modified. That slows down data modifications, but not your queries.
Turn users into a view. The original users table would be renamed, and it loses the avg_service_rating column, which is computed on the fly by the view.
To make the illusion perfect, create an INSTEAD OF INSERT OR UPDATE OR DELETE trigger on the view that modifies the underlying table. Then your application does not need to be changed.
With this solution you pay a certain price both on SELECT and on data modifications, but the latter price will be lower, since you don't have to modify two tables (and users might receive fewer modifications than services). An added advantage is that you avoid data duplication.
A generated column would only be useful if the source data is in the same table row.
Otherwise your options are a view (where you could call a function or calculate the value via a subquery), or an AFTER UPDATE OR INSERT trigger on the service table, which updates users.avg_service_ratings. With a trigger, if you get a lot of updates on the service table you'd need to consider possible concurrency issues, but it would mean the figure doesn't need to be calculated every time a row in the users table is accessed.
I want to trigger on all column changes on a table except a specific one, but listing all the columns in the AFTER INSERT OR UPDATE OF clause is a problem because the table has many columns and the set of columns changes at times, making maintaining the trigger definition in sync very error prone. How can I do this in a way that I just specify the column to omit from the trigger? For the moment I have an event trigger that prints a warning to update the trigger when that table is altered, but that relies on the user noticing the warning and obviously won't help when creating a new db.
In postgresql: multiple sessions want to get one record from the the table, but we need to make sure they don't interfere with each other. I could do it using message queue: put the data in a queue, and them let each session get data from the queue. But is it doable in postgresql? since it will be easier for SQL guys to cal stored procedure. Any way to configure a stored procedure so that no concurrent calling will happen, or use some special lock?
I would recommend making sure the stored procedure uses SELECT FOR UPDATE, which should prevent the same row in the table from being accessed by multiple transactions.
Per the Postgres doc:
FOR UPDATE causes the rows retrieved by the SELECT statement to be
locked as though for update. This prevents them from being modified or
deleted by other transactions until the current transaction ends. That
is, other transactions that attempt UPDATE, DELETE, SELECT FOR UPDATE,
SELECT FOR NO KEY UPDATE, SELECT FOR SHARE or SELECT FOR KEY SHARE of
these rows will be blocked until the current transaction ends. The FOR
UPDATE lock mode is also acquired by any DELETE on a row, and also by
an UPDATE that modifies the values on certain columns. Currently, the
set of columns considered for the UPDATE case are those that have an
unique index on them that can be used in a foreign key (so partial
indexes and expressional indexes are not considered), but this may
change in the future.
More SELECT info.
So you don't end up locking all of the rows in the table at once (i.e. by SELECTing all of the records), I would recommend you use ORDER BY to sort the table in a consistent manner, and then do a LIMIT 1, so that it only gets the next one in the queue. Also add a WHERE clause that checks for a certain column value (i.e. processed), and then once processed set the column to a value that will prevent the WHERE clause from picking it up.
I'm working on an application that imports data from Access to SQL Server 2008. Currently, I'm using a stored procedure to import the data individually by record. I can't go with a bulk insert or anything like that because the data is inserted into two related tables...I have a bunch of fields that go into the Account table (first name, last name, etc.) and three fields that will each have a record in an Insurance table, linked back to the Account table by the auto-incrementing AccountID that's selected with SCOPE_IDENTITY in the stored procedure.
Performance isn't very good due to the number of round trips to the database from the application. For this and some other reasons I'm planning to instead use a staging table and import the data from there. Reading up on my options for approaching this, a cursor that executes the same insert stored procedure on the data in the staging table would make sense. However it appears that cursors are evil incarnate and should be avoided.
Is there any way to insert data into one table, retrieve the auto-generated IDs, then insert data for the same records into another table using the corresponding ID, in a set-based operation? Or is a cursor my only option here?
Look at the OUTPUT clause. You should be able to add it to your INSERT statement to do what you want.
BTW, if you need to output columns into the second table that weren't inserted into the first one, then use MERGE instead of INSERT (as suggested in the comment to the original question) as its OUTPUT clause supports referencing other columns from the source table(s). Otherwise, keeping it with an INSERT is more straightforward, and it does give you access to the inserted identity column.
I'm having experiment to worked out in inserting multiple record into related table using databinding. So, try this!
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