I have a application form that should have been closed last friday. Due to things I can't control, it wasn't closed, and now people have applied after last friday. Unfortunately, those people can't come to the event, so we have to contact them to tell them the bad news.
My problem is, that when I made the form I was too fast and forgot to add a timestamp in the table.
Is there some way (either using php, phpmyadmin or sql-commands) to find out who has applied after a certain time (i.e. when the row was added to the table)?
The Database is a MySQL-database.
Does the table have an autoincrementing ID field?
If so, figure out the value of that ID field for the last person you were able to accept, then use this query in an SQL client like phpmyadmin.
SELECT *
FROM tablename
WHERE tablename.id > last_accepted_id
That will show all the rows for people to which you owe bad news.
This may be possible if you have logging on (not on by default).
Your log file location is configured here in a .conf file.
/etc/*.conf
The logging will be written in that file as..
log=/tmp/yourlogfilename.log
If this is set you can go to that log and see when/what queries where used.
Related
I've got a really horrible problem on my hands, for some reason data is being wiped from a particular table's column and I have no idea why.
The table is called events. Inside the table there are a number of columns, name, date etc however recently I put a field in called 'schedule' this is of type TEXT.
On the web page, you can edit the event in different tabs and create a schedule (fields using jQuery clone / etc) and then when the schedule data gets saved into th database the HTML $_POST data gets converted into a JSON array using json_encode:
$db->prepared['schedule'] = json_encode(
array(
"scheduleday" => ($_POST['scheduleday'] ?? array()),
"scheduletime" => ($_POST['scheduletime'] ?? array()),
"scheduledescription" => ($_POST['scheduledescription'] ?? array()),
"schedulevenue" => ($_POST['schedulevenue'] ?? "")
)
);
The resulting json array could look like this, for example:
{"scheduleday":{"1":"2020-08-25","2":"2020-08-26"},"scheduletime":{"1":["19:30","20:00 - 20:50"],"2":["14:00 - 14:50","14:50 - 15:00","15:00 - 15:50","15:50 - 16:00","16:00 - 16:50"]},"scheduledescription":{"1":["Introduction","John Smith"],"2":["John Smith","Break","John Smith teaching","Break","John Smith teaching"]},"schedulevenue":"1 Acia Avenue"}
Straight after this is INSERTED or UPDATEd into the mysql database it is then sent to a function that uses fpdf to turn the json array into a PDF which can be downloaded.
This works well, apart from one problem. Random (or what appears to be random) schedules are going missing. We can create a schedule one day and then a week later, or a few days later, suddenly the file will have been deleted and the column in the table removed. No other data in the table is getting deleted, nothing apart from the schedule.
Here's what I've tried to find out whats going on:
SQL Trigger
I've set a trigger on the event table which dumps data into a table called event_trigger AFTER an update is run. This is the code for the trigger:
BEGIN
INSERT INTO `event_trigger` (oldID,name,old_schedule,new_schedule) VALUES
(OLD.id,
OLD.name,
OLD.schedule,
NEW.schedule);
END
This has been helpful in the sense that I now know if there is an event with a schedule missing, because the NEW.schedule will be empty. However that last two times a schedule has gone missng (yesterday and today, in fact) its been outside of office hours, 18:45 and 19:22 so no one should be performing any updates on events in those times.
.txt File Log
The other thing i've done is on the page where the events are updated I've put a text log, which dumps the prepared variables, the SQL statement and the user and the user ID to a text file. Unfortunately this isnt working because when a schedule goes missing, its not getting logged in there. All that tells me is that its happening somewhere else.
I dont know how to narrow this down further. There is no user activity at the times when an event is deleted. The closest i've gotten is using the TRIGGER. But I am so limited as the information from the trigger is not enough; I can't get IP, SQL statement, user ID or anything like that. Just the OLD and NEW variables.
Can anyone help me think of ways to investigate, I'd be so grateful. This has been going on for over a month now, and its infuriating because I just cannot see why it is happening.
The only extra option I can think of doing is turning on full SQL logs, but I am reluctant to do that as it will slow the server down immensly.
Have you examined your web server's logs? If this data corruption comes in via your web application, you should be able to see the exact time and originating IP address of the unfortunate event. You may also be able to figure out which page of your web app caused the problem.
To track things down more accurately in your database server, add, to your event_trigger table, these columns:
timestamp (when the trigger fired)
user (the MySQL host and user that issued the UPDATE that fired the trigger)
query (the text of the UPDATE query)
Then change your trigger to say
BEGIN
INSERT INTO event_trigger
(oldID,name,old_schedule,new_schedule, ts, user, query)
VALUES
(OLD.id,
OLD.name,
OLD.schedule,
NEW.schedule,
NOW(),
CURRENT_USER(),
(SELECT INFO FROM information_schema.process_list WHERE id=CONNECTION_ID())
);
END
Then, your event_trigger table will show you the user webapp#localhost or cybercreep#cracker.example.com that issued the UPDATE, when it was issued, and what the exact query was.
(With the exact query you can search your code base to try to track down what function is running amok.)
Once you know what database user is issuing the query, you can consider suspending access for that particular user after business hours, and see who complains. But keep in mind that the database user is probably the generic username used by your web application, so it may not tell you much.
It's very likely that this is a legitimate web app user misusing, by mistake, your system.
Pro tip : Put automatic timestamp columns in all your application tables so you can keep track of changes. Add
ts TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
columns to your tables, and MySQL takes care of updating them.
Pro tip 2 (harder) add an action log table to your database, and make your web app insert a row to it each time a user takes an action. Then you can run queries like "who did what yesterday between 19:00 and 19:30?" Customer support people love to be able to do that.
This question already has answers here:
How to make sure there is no race condition in MySQL database when incrementing a field?
(2 answers)
Lock file/content while being edited in browser.
(1 answer)
Closed 4 years ago.
I've developed a web application using Apache, MySQL and PHP.
This web app allows multiple users' to login to the application.
Then, through the application, they have access to the Database.
Since race conditions may apply when two or more users try to SELECT/UPDATE/DELETE the same information (in my case a row of a Table), I am searching for the best way to avoid such race conditions.
I've tried using mysqli with setting autocommit to OFF and using SELECT .... FOR UPDATE, but this fails to work as -to my understanding- with PHP, each transaction commits automatically and each connection to the db is being auto released when the PHP -->html page is provided/loaded for the user.
After reading some posts, there seem to be two possible solutions for my problem :
Use PDO. To my understanding PDO creates connections to the DB which are not released when the html page loads. Special precautions should be taken though as locks may remain if e.g. the user quits the page and the PDO connection has not been released...
Add a "locked" column in the corresponding table to flag locked rows. So e.g. when an UPDATE transaction may only be performed if the corresponding user has locked the row for editing. The other users shall not be allowed to modify.
The main issue I may have with PDO is that I have to modify the PHP code in order to replace mysqli with PDO, where applicable.
The issue with the scenario 2 is that I need to also modify my DB schema, add additional coding for lock/unlock and also consider the possibility of "hanging" locked rows which may result in additional columns to be added in the table (e.g. to store the time the row was locked and the lockedBy information) and code as well (e.g. to run a Javascript at User side that will be updating the locked time so that the user continuously flags the row while using it...)
Your comments based on your experience would be highly appreciated!!!
Thank you.
It might be an opinion instead of a technical answer, but too long to write it as a comment.
I want to think it like booking a seat in a movie or a flight: When an user selects a seat and presses next, the seat will be reserved for that user for a certain amount of time, and when user doesn't finish in the given time, it gets a timeout exception without processing further. You can use an edit button besides the row, and when the user clicks it, on the server side, you check if the row is reserved to someone else, and if not, reserve it to the user. Other users won't get an edit form when they also click the edit button after that user. I don't know how database systems handle this though.
But, one way to make it sure, re-read the row after user edits and commits it to display the user. If any lock mechanism prevented the row from being updated, the user will also know it by not seeing the change in the row.
I've been reading through several topics now and did some research about logging changes to a mysql table. First let me explain my situation:
I've a ticket system with a table: 'ticket'
As of now I've created triggers which will enter a duplicate entry in my table: 'ticket_history' which has "action" "user" and "timestamp" as additional columns. After some weeks and testing I'm somewhat not happy with that build since every change is creating a full copy of my row in the history table. I do understand that disk space is cheap and I should not worry about it but in order to retrieve some kind of log or nice looking history for the user is painful, at least for me. Also with the trigger I've written I get a new row in the history even if there is no change. But this is just a design flaw of my trigger!
Here my trigger:
BEFORE UPDATE ON ticket FOR EACH ROW
BEGIN
INSERT INTO ticket_history
SET
idticket = NEW.idticket,
time_arrival = NEW.time_arrival,
idticket_status = NEW.idticket_status,
tmp_user = NEW.tmp_user,
action = 'update',
timestamp = NOW();
END
My new approach in order to avoid having triggers
After spening some time on this topic I came up with an approach I would like to discuss and implement. But first I would have some questions about that:
My idea is to create a new table:
id sql_fwd sql_bwd keys values user timestamp
-------------------------------------------------------------------------
1 UPDATE... UPDATE... status 5 14 12345678
2 UPDATE... UPDATE... status 4 7 12345678
The flow would look like this in my mind:
At first I would select something or more from the DB:
SELECT keys FROM ticket;
Then I display the data in 2 input fields:
<input name="key" value="value" />
<input type="hidden" name="key" value="value" />
Hit submit and give it to my function:
I would start with a SELECT again: SELECT * FROM ticket;
and make sure that the hidden input field == the value from the latest select. If so I can proceed and know that no other user has changed something in the meanwhile. If the hidden field does not match I bring the user back to the form and display a message.
Next I would build the SQL Queries for the action and also the query to undo those changes.
$sql_fwd = "UPDATE ticket
SET idticket_status = 1
WHERE idticket = '".$c_get['id']."';";
$sql_bwd = "UPDATE ticket
SET idticket_status = 0
WHERE idticket = '".$c_get['id']."';";
Having that I run the UPDATE on ticket and insert a new entry in my new table for logging.
With that I can try to catch possible overwrites while two users are editing the same ticket in the same time and for my history I could simply look up the keys and values and generate some kind of list. Also having the SQL_BWD I simply can undo changes.
My questions to that would be:
Would it be noticeable doing an additional select everytime I want to update something?
Do I lose some benefits I would have with triggers?
Are there any big disadvantages
Are there any functions on my mysql server or with php which already do something like that?
Or is there might be a much easier way to do something like that
Is maybe a slight change to my trigger I've now already enough?
If I understad this right MySQL is only performing an update if the value has changed but the trigger is executed anyways right?
If I'm able to change the trigger, can I still prevent somehow the overwriting of data while 2 users try to edit the ticket the same time on the mysql server or would I do this anyways with PHP?
Thank you for the help already
Another approach...
When a worker starts to make a change...
Store the time and worker_id in the row.
Proceed to do the tasks.
When the worker finishes, fetch the last worker_id that touched the record; if it is himself, all is well. Clear the time and worker_id.
If, on the other hand, another worker slips in, then some resolution is needed. This gets into your concept that some things can proceed in parallel.
Comments could be added to a different table, hence no conflict.
Changing the priority may not be an issue by itself.
Other things may be messier.
It may be better to have another table for the time & worker_ids (& ticket_id). This would allow for flagging that multiple workers are currently touching a single record.
As for History versus Current, I (usually) like to have 2 tables:
History -- blow-by-blow list of what changes were made, when, and by whom. This is table is only INSERTed into.
Current -- the current status of the ticket. This table is mostly UPDATEd.
Also, I prefer to write the History directly from the "database layer" of the app, not via Triggers. This gives me much better control over the details of what goes into each table and when. Plus the 'transactions' are clear. This gives me confidence that I am keeping the two tables in sync:
BEGIN; INSERT INTO History...; UPDATE Current...; COMMIT;
I've answered a similar question before. You'll see some good alternatives in that question.
In your case, I think you're merging several concerns - one is "storing an audit trail", and the other is "managing the case where many clients may want to update a single row".
Firstly, I don't like triggers. They are a side effect of some other action, and for non-trivial cases, they make debugging much harder. A poorly designed trigger or audit table can really slow down your application, and you have to make sure that your trigger logic is coordinated between lots of developers. I realize this is personal preference and bias.
Secondly, in my experience, the requirement is rarely "show the status of this one table over time" - it's nearly always "allow me to see what happened to the system over time", and if that requirement exists at all, it's usually fairly high priority. With a ticketing system, for instance, you probably want the name and email address of the users who created, and changed the ticket status; the name of the category/classification, perhaps the name of the project etc. All of those attributes are likely to be foreign keys on to other tables. And when something does happen that requires audit, the requirement is likely "let me see immediately", not "get a database developer to spend hours trying to piece together the picture from 8 different history tables. In a ticketing system, it's likely a requirement for the ticket detail screen to show this.
If all that is true, then I don't think history tables populated by triggers are a good idea - you have to build all the business logic into two sets of code, one to show the "regular" application, and one to show the "audit trail".
Instead, you might want to build "time" into your data model (that was the point of my answer to the other question).
Since then, a new style of data architecture has come along, known as CQRS. This requires a very different way of looking at application design, but it is explicitly designed for reactive applications; these offer much nicer ways of dealing with the "what happens if someone edits the record while the current user is completing the form" question. Stack Overflow is an example - we can see, whilst typing our comments or answers, whether the question was updated, or other answers or comments are posted. There's a reactive library for PHP.
I do understand that disk space is cheap and I should not worry about it but in order to retrieve some kind of log or nice looking history for the user is painful, at least for me.
A large history table is not necessarily a problem. Huge tables only use disk space, which is cheap. They slow things down only when making queries on them. Fortunately, the history is not something you'd use all the time, most likely it is only used to solve problems or for auditing.
It is useful to partition the history table, for example by month or week. This allows you to simply drop very old records, and more important, since the history of the previous months has already been backed up, your daily backup schedule only needs to backup the current month. This means a huge history table will not slow down your backups.
With that I can try to catch possible overwrites while two users are editing the same ticket in the same time
There is a simple solution:
Add a column "version_number".
When you select with intent to modify, you grab this version_number.
Then, when the user submits new data, you do:
UPDATE ...
SET all modified columns,
version_number=version_number+1
WHERE ticket_id=...
AND version_number = (the value you got)
If someone came in-between and modified it, then they will have incremented the version number, so the WHERE will not find the row. The query will return a row count of 0. Thus you know it was modified. You can then SELECT it, compare the values, and offer conflict resolution options to the user.
You can also add columns like who modified it last, and when, and present this information to the user.
If you want the user who opens the modification page to lock out other users, it can be done too, but this needs a timeout (in case they leave the window open and go home, for example). So this is more complex.
Now, about history:
You don't want to have, say, one large TEXT column called "comments" where everyone enters stuff, because it will need to be copied into the history every time someone adds even a single letter.
It is much better to view it like a forum: each ticket is like a topic, which can have a string of comments (like posts), stored in another table, with the info about who wrote it, when, etc. You can also historize that.
The drawback of using a trigger is that the trigger does not know about the user who is logged in, only the MySQL user. So if you want to record who did what, you will have to add a column with the user_id as I proposed above. You can also use Rick James' solution. Both would work.
Remember though that MySQL triggers don't fire on foreign key cascade deletes... so if the row is deleted in this way, it won't work. In this case doing it in the application is better.
I have 2 sql servers on 2 diferent locations.
One is a web server and the other a crm system.
People update and register on web, when they do changes i need to insert or update the changes to my crm server.
I have a view on web server where i can select from but i need to
insert into on duplicate update only fields that changed and then in a description
show
wich fields were updated?
I have no clue how to start.
You can not determine the differences on fields after changing them.
You can however select and store the contents prior to the update and then compare it with the new contents.
The question then becomes: Do you need the differences per column?
If yes: Pre-select and do the difference yourself (in the
application).
If no: Use the method described by #Ogelami (and accept his answer :)
On a side note: The Pre-Select thing won't work as well, when you start using several mysql servers, since you might run into issues with drifting data (ie one server is behind in inserted data). When this occurs, the method will get a bit more complex.
Perhaps something like this?
INSERT INTO table ON DUPLICATE UPDATE table SET field = value WHERE field != 'value'
and you might want to look into this to see if there are Affected rows.
Google unfortunately didn't seem to have the answers I wanted. I currently own a small search engine website for specific content using PHP GET.
I want to add a latest searches page, meaning to have each search recorded, saved, and then displayed on another page, with the "most searched" at the top, or even the "latest search" at the top.
In short: Store my latest searches in a MySQL database (or anything that'll work), and display them on a page afterwards.
I'm guessing this would best be accomplished with MySQL, and then I'd like to output it in to PHP.
Any help is greatly appreciated.
Recent searches could be abused easily. All I have to do is to go onto your site and search for "your site sucks" or worse and they've essentially defaced your site. I'd really think about adding that feature.
In terms of building the most popular searches and scaling it nicely I'd recommend:
Log queries somewhere. Could be a MySQL db table but a logfile would be more sensible as it's a log.
Run a script/job periodically to extract/group data from the log
Have that periodic script job populate some table with the most popular searches
I like this approach because:
A backend script does all of the hard work - there's no GROUP BY, etc made by user requests
You can introduce filtering or any other logic to the backend script and it doesn't effect user requests
You don't ever need to put big volumes of data into the database
Create a database, create a table (for example recent_searches) and fields such as query (the query searched) and timestamp (unix timestamp that the query was made) said, then for your script your MySQL query will be something like:
SELECT * FROM `recent_searches` ORDER BY `timestamp` DESC LIMIT 0, 5
This should return the 5 most recent searches, with the most recent one appearing first.
Create table (something named like latest_searches) with fields query, searched_count, results_count.
Then after each search (if results_count>0), check, if this search query exists in that table. And update or insert new line into table.
And on some page you can just use data from this table.
It's pretty simple.
Ok, your question is not yet clear. But I'm guessing that you mean you want to READ the latest results first.
To achieve this, follow these steps:
When storing the results use an extra field to hold DATETIME. So your insert query will look like this:
Insert into Table (SearchItem, When) Values ($strSearchItem, Now() )
When retrieving, make sure you include an order by like this:
Select * from Table Order by When Desc
I hope this is what you meant to do :)
You simply store the link and name of the link/search in MySQL and then add a timestamp to record what time sb searched for them. Then you pull them out of the DB ordered by the timestamp and display them on the website with PHP.
Create a table with three rows: search link timestamp.
Then write a PHP script to insert rows when needed (this is done when the user actually searches)
Your main page where you want stuff to be displayed simply gets the data back out and puts them into a link container $nameOfWebsite
It's probably best to use a for/while loop to do step 3
You could additionally add sth like a counter to know what searches are the most popular / this would be another field in MySQL and you just keep updating it (increasing it by one, but limited to the IP)