I have been searching for a way that can help me notify the C code about successful INSERT operation fired over a Mysql table.
So the insert query is already there in other component code, now in an independent component I want to get notified when Insert on a particular table takes place so that I could fire select on the table. Currently I fire select query on particular interval, need to avoid that and instead do it after an insert query.
Don't give users INSERT privilege to tables. Instead, make the go through an API -- either a Stored Procedure or a client API. There do any monitoring/etc you need.
Note that MySQL cannot (for security reasons) launch anything outside itself -- no email, callbacks, etc. There is an exception: UDFs (User Defined Functions).
Related
Hypothetically, I am going to develop a trigger that inserts a record to Table A when an insertion made to an Table A.
Therefore, I want to know how the system handles that kind of loophole or it is going to continue as a loop until the system hangs which requires restart and possibly remove the DB.
I'm trying to gather information on almost every DBMS on this issue or loophole.
I can only speak to Oracle, I know nothing of MySQL.
In Oracle, this situation is known as mutation. Oracle will not spiral into an endless loop. It will detect the condition, and raise an ORA-04091 error.
That is:
ORA-04091: table XXXX is mutating, trigger/function may not see it
The standard solution is to define a package with three functions and a package level array. The three functions are as follows:
initialize - this will only zero out the array.
save_row - this will save the id of the current row (uk or pk) into the arrray.
process_rows - this will go through the array, and actually do the trigger action for each row.
Now, define some trigger actions:
statement level BEFORE: call initialize
row level BEFORE or AFTER: call save_row
statement level AFTER: call process_rows
In this way, Oracle can avoid mutation, and your trigger will work.
More details and some sample code can be found here:
https://asktom.oracle.com/pls/asktom/ASKTOM.download_file?p_file=6551198119097816936
You can only insert a record in same table if you are using instead of trigger. In all other cases you can only modify the record being inserted.
I hope this answers your quest.
you can create trigger in mysql DBMS.
check below link for create insert trigger syntex
http://www.techonthenet.com/oracle/triggers/after_insert.php
My use case is that I have a MYSQL table which has a change tracking table behind it. Both tables are InnoDB.
I'd like to use triggers to enforce two things.
One: forcing a copy to be made of previous state on every update (update trigger performs insert select query) This is non-trivial and I have already done it.
Two: limit access to the second table to read only for users, while triggers can still insert/update/delete as necessary
Further research on user access and triggers has dug up this:
Mysql 5.5 reference manual: 19.6 Access Control for Stored Programs and Views
Turns out that stored programs can be assigned a user to run as. Triggers are stored programs. By restricting Insert, Update, and Delete to a special user which only will be used by a trigger and using the DEFINER attribute of the trigger (or any stored program) I can make the trigger which I want to have access run under that user.
I have a table (items in stock) which gets updated from several applications.
All queries are supposed to also set a field 'src' with some audit information (user and form), but some queries are not doing that.
I intend to create a trigger on update, which checks if the 'src' field is changed.
I would like to rollback the update and fire an error if the 'src' is not set, but also to log the query, so I better can identify the offending application.
Is the actual query text available to the trigger?
Or any other identifier?
All connections to the database are done via scripts on webservers, with one of two logins, but from a handfull of servers, so the ip of the server might be useful.
The connection information available is:
select *
from sys.dm_exec_connections as EC inner join
sys.dm_exec_sessions as ES on ES.session_id = EC.session_id
where EC.session_id = ##SPID
AFAIK you cannot get the triggering statement within a trigger.
I have so many tables in my DB.
eg. user, organisation,etc.
**User**
userId,name,age,orgId,etc..
**SessionLog**
logId, userId, operations, reason
If one admin makes changes like inserting, updating ,deleting, I will log every operations in SessionLog table WHAT he made.
So I plan to use Trigger.But the problem is I want to log the userId for WHO too. By using Trigger WHAT is OK. But for logging WHO, how can I do ?
1) do I need to retrieve the logId and need to update the row with WHO?
or
2) just use the simple INSERT statement to log everything? which way is better?
3) Is there any way to pass desired parameters to Trigger?
Thanks.
1. User
You can use CURRENT_USER to get this. http://dev.mysql.com/doc/refman/5.0/en/information-functions.html#function_current-user
2. Insert statement vs. Trigger
A trigger will abstract logging away from everybody else, and usually is the easiest solution that stays hidden.
INSERTS / UPDATES will not return until the trigger has completed.
Therefore while triggers on tables with light activity is an OK idea, it will become a real hindrance when dealing with tables that have a lot of activity.
Another option is to encapsulate this in the data access layer, but if you have even a single user that has direct access to the data (DBA included) then I do not recommend this approach.
I've been hearing about triggers, and I have a few questions.
What are triggers?
How do I set them up?
Are there any precautions, aside from typical SQL stuff, that should be taken?
Triggers allow you to perform a function in the database as certain events happen (eg, an insert into a table).
I can't comment on mysql specifically.
Precaution: Triggers can be very alluring, when you first start using them they seem like a magic bullet to all kinds of problems. But, they make "magic" stuff happen, if you don't know the database inside out, it can seem like really strange things happen (such as inserts into other tables, input data changing, etc). Before implementing things as a trigger I'd seriously consider instead enforcing the use of an API around the schema (preferably in the database, but outside if you can't).
Some things I'd still use triggers for
Keeping track of "date_created" and "date_last_edited" fields
Inserting "ID"'s (in oracle, where there is no auto id field)
Keeping change history
Things you wouldn't want to use triggers for
business rules/logic
anything which connects outside of the database (eg a webservice call)
Access control
Anything which isn't transactional ( anything you do in the trigger MUST be able to rollback with the transaction )
From dev.mysql.com, a trigger is
...a named database object that is
associated with a table and that is
activated when a particular event
occurs for the table.
The syntax to create them is also documented at that site.
Briefly,
CREATE
[DEFINER = { user | CURRENT_USER }]
TRIGGER trigger_name trigger_time trigger_event
ON tbl_name FOR EACH ROW trigger_stmt
And they provide an example:
CREATE TABLE account (acct_num INT, amount DECIMAL(10,2));
CREATE TRIGGER ins_sum BEFORE INSERT ON account FOR EACH ROW SET #sum = #sum + NEW.amount;
You at least need to abide by all the restrictions on stored functions.
You won't be able to lock tables, alter views, or modify the table that triggered the trigger. Also triggers may cause replication problems.
A trigger is a named database object that is associated with a table and that is activated when a particular event occurs for the table.
To create a trigger:
CREATE TRIGGER triggerName [BEFORE|AFTER] [INSERT|UPDATE|DELETE|REPLACE] ON tableName FOR EACH ROW SET stuffToDoHERE;
Even though I answered this part the other question still stands.
This question is old and other answers are very good, but since the user asked about precautions that should be taken, I want to add something:
If you use replication in a complex environment, don't make a massive use of Triggers, and don't call stored procedures from triggers.
Triggers are slow in MySQL.
You can't use some SQL statements within triggers. And some statements are permitted but should be avoided, like LOCK. The general rule is: if you don't fully understand the implications of what you are doing, you shouldn't do it.
Triggers can cause endless loops, so be careful.