I have a problem debugging some problem.
I started thread in wordpress.stackexchange.com thinking that I get more wordpress related debugging suggestions but went with totally different way.
You can see topic here: https://wordpress.stackexchange.com/questions/123394/some-ways-to-debug-code
with update: DELETE FROM wp_bp_activity WHERE item_id = 0
My Question is SQL related: Can DELETE statement be triggered from something then DELETE query? for example I rememeber having a bad query which was deleting everything. (but that was everything and not an if statment)
So to extend this question: If I search every query with DELETE FROM will I find it for sure? Can this be written differently? Because for now, I can't find it.
TRUNCATE is also used to DELETE all the records from a table.
You can also have some kind of foreign key cascading, that is triggering the delete in that table. More here.
Addicionally, make sure to search on the database also, on triggers and on stored procedures
One other option is that they were updated to a different value than the one you are looking for.
Related
I have several databases that are used by several applications (one of which is our own, the others we have no control over in what they do).
Out software has to know when the database has last been changed. For reasons I won't get into to keep this short we decided that going with a new table per database that has a singular field: last_changed_on that has a GetDate() as a value. This way our own software can check when it was last changed and check it to the date it has stored for said database and do things if the date is newer than what is stored in-memory.
After doing some research we decided that working with Triggers was the way to go, but from what I could find online, triggers look at specific columns that you set for Updates.
What I'd like to know is if there is a way to automate the process or just have a trigger that happens whenever anything happens insert, update, remove wise?
So I am looking for something like this:
CREATE TRIGGER LastModifiedTrigger
ON [dbo].[anytable]
AFTER INSERT, UPDATE, DELETE
AS
INSERT INTO dbo.LastModifiedTable (last_modified_on) VALUES (CURRENT_TIMESTAMP)
I know that the above example isn't a correct trigger, I'm rather new to them so I was unsure on how to word it.
It might be interesting to note that I can have my own software run several queries creating the queries automatically for each table and each column, but I'd rather avoid to do that as keeping track of all those triggers will be a pain in the long run.
I'd prefer to have a little triggers per database as possible, if only by not having to make a trigger for each individual column name.
Edit: To clarify: I am trying to avoid having to create an automated script that goes and scans every table, and sequentially every column of every table, to create a trigger to see if something is changed there. My biggest issue at the moment is the trigger behavior on updates, but I'm hoping to avoid having to specify tables as well for insert and delete
Edit 2: To avoid future confusion, I'm looking for a solution to this problem for both SQL Server (MS SQL/T SQL) and MySQL
Edit 3: Turns out that I read the documentation very wrongly and (at least on MySql) the trigger activates on any given updated column without having to define a specific one. Regardless, I'm still wondering if there is a way to just have less triggers than having one for each table in a database. (i.e. 1 for any type of update(), 1 for any type of insert(), and 1 for any type of delete()
EDIT 4: Forgot that the argument for overwriting 1 field will come with performance issues, I've considered this and I'm now working with multiple rows. I've also handled the creating of 3 triggers (insert(), update(), and delete()) for each database through my software's code, I really wished this could've been avoided, but it cannot.
Solution
After a bunch more digging on the internet and keep finding opposite results of what I was looking for, and a bunch of trial and error, I found a solution.
First and foremost: having triggers not being dependent on a table (aka, the trigger activates for every table is impossible, it cannot be done, which is too bad, it would've been nice to keep this out of the program code, but nothing I can do about it.
Second: the issue for updates on not being column specific was an error due to my part for searching for triggers not being dependent on specific columns only giving me examples for triggers that are.
The following solution works for MySql, I have yet to test this on SQL Server, but I expect it to not be too different.
CREATE TRIGGER [tablename]_last_modified_insert
AFTER INSERT/UPDATE/DELETE ON [db].[tablename]
FOR EACH ROW
BEGIN
INSERT INTO [db].last_modified(last_modified_on)
VALUES(current_timestamp())
END
As for dynamically creating these triggers, the following show how I get it to work:
First Query:
SHOW TABLES
I run the above query to get all the tables in the database, exclude the last_modified I made myself, and loop through all of them, creating 3 triggers for each.
A big thank you to Arvo and T2PS for their replies, their comments helped by pointing me in the right direction and writing up the solution.
You're slightly off in the assumption that SQL Server triggers are per-column; the CREATE TRIGGER syntax binds the trigger to the named table for the specified operations. The trigger will be called with two logical tables in scope (inserted & deleted) that contain the rows modified by the operation that caused the trigger to fire; if you wanted to check for specific columns' values or changes, then the trigger logic would need to operate against those logical tables.
If you take this approach, you will need to create a trigger for each table you wish to monitor in this fashion; we've had a similar need to track changes (at a more granular level), we didn't find a "pseudotable" that corresponds to all tables in a schema/database. You should also be aware that locking semantics will come into play by doing this, as you will have triggers from multiple tables all targeting the same row for an update as part of separate operations -- depending on the concurrency model in effect, you could be looking at performance consequences by doing so if you expect multiple DML queries to operate concurrently against your database.
I would suggest checking Arvo's commented link above for suitability instead; querying system views is more likely to avoid contention (and other performance-related) issues from using triggers in your scenario.
After a bunch more digging on the internet and keep finding opposite results of what I was looking for, and a bunch of trial and error, I found a solution.
First and foremost: having triggers not being dependent on a table (aka, the trigger activates for every table is impossible, it cannot be done, which is too bad, it would've been nice to keep this out of the program code, but nothing I can do about it.
Second: the issue for updates on not being column specific was an error due to my part for searching for triggers not being dependent on specific columns only giving me examples for triggers that are.
The following solution works for MySQL, I have yet to test this on SQL Server, but I expect it to not be too different.
CREATE TRIGGER [tablename]_last_modified_insert
AFTER INSERT/UPDATE/DELETE ON [db].[tablename]
FOR EACH ROW
BEGIN
INSERT INTO [db].last_modified(last_modified_on)
VALUES(current_timestamp())
END
As for dynamically creating these triggers, the following show how I get it to work:
First Query:
SHOW TABLES
I run the above query to get all the tables in the database, exclude the last_modified I made myself, and loop through all of them, creating 3 triggers for each.
Perhaps you could use Audit for SQL Server:
CREATE SERVER AUDIT [ServerAuditName]
TO FILE
(
FILEPATH = N'C:\Program Files......'
)
ALTER SERVER AUDIT [ServerAuditName] WITH (STATE=ON)
GO
CREATE DATABASE AUDIT SPECIFICATION [mySpec]
FOR SERVER AUDIT [ServerAuditName]
ADD (INSERT, UPDATE, DELETE ON DATABASE::databasename BY [public])
WITH (STATE=ON)
GO
Then you can query for changes:
SELECT *
FROM sys.fn_get_audit_file ('C:\Program Files......',default,default);
GO
We have a scenario where a long running query is updating a table is blocking a query attempting an update to update a completely different table. I see plenty of examples of how to find blocking queries, but in this case I do not see anything that helps me understand why an update to tableA would be blocking an update to tableB.
How can I begin to understand blocking like this?
I have a table with 120 columns. I need to set up audit trail which would log any column if it was changed. As it is now, I guess I have to set up a trigger with condition something like this for every column:
IF(NEW.columnName != OLD.columnName)
THEN //log the old value
This would need to be done 120 times... While I would have accepted this approach 20 years ago, today I refuse to believe it's impossible to automate such a simple procedure finding changed columns automatically.
This is what I discovered so far:
Neither NEW nor OLD is a table, it's a sort of a language construct, therefor you can't do "SELECT NOW.*" or something similar.
Dynamic SQL is not allowed in triggers (this could have solved the problem).
Procedures using dynamic SQL are not allowed in triggers (seriously, Oracle, it looks like you have worked really hard to disable this feature no matter what).
I was thinking to use BEFORE and AFTER triggers in conjunction with temporary tables and variables which would have possibly solved the problem, however yet again dynamic SQL would be required. I feel like I hit a dead end.
Is there a solution to this at all?
A side question: would this be possible in PostgreSQL?
UPDATE: I found 2 potential solutions however neither of them look clear enough to me:
using EVENTS as a workaround to use triggers in conjunction with dynamic SQL workaround. I have to admit, I don't quite get this, does this mean that EVENT fires every second no matter what?
This article says that it is possible to use dynamic SQL inside trigger as long as temporary table is used with it. That is still using dynamic SQL, so I don't quite understand.
interesting, I was facing the same problem couple of years ago with implementing dynamic trigger-based audit log. The solution I came up with was to simply generate the SQL trigger code which then can be (automatically) applied to replace old trigger definitions. If memory serves, I created few SQL templates which were processed by a PHP script which in turn was outputting complete trigger definitions based on "SELECT COLUMN_NAME FROM information_schema.COLUMNS WHERE ..." Yes, the trigger code was huge, but it worked! Hope that helps a little =)
i did this for one of the projects by creating a shadow table. if you are not dealing with millions of updates, this might work
when the user logs in, SET #user_id = { logged in user id }
create a trigger on the table before update to copy the row to be modified to a shadow table with the same structure ( note that you cannot have a primary key in the shadow table nor unique keys )
add additional columns to the shadow table ( modified_by, modified_on )
create a small php script to show the diff between columns - this way you dont touvh the existing php code base
if you are dealing with lots of updates and want to keep the shadow table small, a cron can be written to parse the shadow table and identify which column changed and only store this info to another table
Once a record is entered in a particular table, I think I don't ever want it to be deleted. The records are there to keep track of things for historical purposes. I'm using MySQL, InnoDB. Is there any way I can protect that table from accidental deletes by the application layer? If so, is this a good approach?
If you can set the permission for your user(s), don't give the delete permission. There're situations where this practice is a "must be" like the tables for statistics purpose. Thus, if your table is used to achieve one of this goal, it's a good approach.
I use a trigger that detects the deletion and does some illegal stuff so the whole operation fails. For example like this:
CREATE TRIGGER protect_delete before delete ON protected_table
FOR EACH ROW UPDATE non_existing_table SET non_existing_column=1;
So when someone will attempt a delete operation - the whole statement will fail. You also might use better names for non_existing_column and non_existing_table.
E.g it is possible to obtain an error message like this:
ERROR 1146 (42S02): Table 'database.delete_restricted_on_tableX'
doesn't exist
EDIT: also it is possible to create even better fail messages, please check here http://www.brokenbuild.com/blog/2006/08/15/mysql-triggers-how-do-you-abort-an-insert-update-or-delete-with-a-trigger/
One other option is switch to the ARCHIVE engine for historical tables.
This will prevent any DELETE or UPDATE actions on the table, and compress the data. One (major) downside to this approach is that you cannot index the columns on the table.
I think you should implement this logic in your application layer and insert a column where you put a no-delete flag.
Another idea would be to exclude the delete access for the db user
You may want to write a trigger that detects the deletion, then reinserts the record, but there may be some issues with that, so you can also just add a foreign key constraint that will prevent the deletion.
For some discussions on this you can look at: http://rpbouman.blogspot.com/2011/10/mysql-hacks-preventing-deletion-of.html.
I am fairly new to using mysql. I have an application that performs some basic querying. I am also trying to run a simple delete statement -
delete from mydb.mytable
This table is a simple 2 column table with not keys or triggers or anything defined. For some reason, the delete is not being performed. If I run the statement from MySql Workbench in the query window, it works fine. From the code, it does nothing. I am not seeing any error messages. I created a user with select, insert, update and delete rights to the schema. I am able to do the insert fine, but the delete does not seem to be working.
Is there a setting for mysql that I am missing that will not allow me to perform the delete?
Thanks for any thoughts.
Fist of all, check if
you are connected to the right database ;
you are using transaction and forgetting 'commit' ;
the user you use have enough permissions to delete from the table .
As a side notice, if you want to delete all records, you should use truncate instead of delete
Are you using transactions? My first guess is that your code might be issuing a BEGIN TRANSACTION without a COMMIT.
We would have to see some of your code to answer the question.
My guess is that you are not calling commit from your code. You can configure MySQL to auto-commit your queries, but this is usually not what you want.