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.
Related
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 seen some really old posts that somehow address my question but they werent answered.
I usually update mysql tables regardless of a column's change. However, in this new project am starting to work on, I am concerned about that practice. The update is per single row mostly but updates do happen very often.
What would be the proper way to handle the case? Have hidden fields per columns then compare with php or Javascript? Can MySQL be smarted to doing something like this? Which costs more: writing to mysql table even when a column needs no update or to check with php for every update?
Any insight is appreciated. Thanks.
it is possible to create column at run time in mysql table using add column in php.
but how to insert data at run time into the newly created field(s) (i.e.column(s))?
thanks in advance
EDIT:
some said that why i need to create a new column at run time as i know before hand that the column will be necessary. No, columns quite unknown at the beginning may be needed to be created Just take the problem as a programming issue.
PLZ GIVE THE EXPLANATION OF -VE RATING
i donno why my post was rated -ve ly. uff where is the solution to the prob that someone needs to create columns in a mysql table beforehand and the thing is quite unpredictable. Suppose a site admin needs to add column to a membership club table from time to time. Can't this be any real situation? Why is there no explanation of -ve rating , plz?
Oh that,
You know you need to create the address column already. Then what you need to do is do a 2 step registration.
You need to check whether this column is empty when the student logs in. If it is empty then you ask the student to put in their address. When they have typed in the address the just update the column and change it from blank to the address provided by the student. You dont need the dynamic columns as that would be slow and complex operation.
Check database for the address of the student or check if the user is loggin in the first time
If the users address is empty or the user is logging in the first time
Then
Ask the user for their address
If the address is given then
Update the address column with the provided address
Endif
Endif
Done
Yes, you can execute a MySQL command in PHP code to add a column, create a table, alter a table and more.
Use a function that alters your table and which returns true, if the altering was successfull. If you get this, you can use normal UPDATE functions.
But you should never, never, never design your application this way. Think about all the ibformations, that you will get now and in the future. Then design your tables referring to this informations.
In your special case you already know, that you will aks for the address informations, so implement this NOW in your code. user658911 showed you how to do this.
In the future it might be neccessary to add more columns or tables to your system, because the requirements will change. If so, you can realize those changes on your development system, test them with your current database content and after all deploy it to your production system.
Altering a table during runtime should never be an option.
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)
I'm trying to setup a (I thought) fairly simple versioning system for static html pages on a site. The goal is to keep previous versions of the content, then restore to them if needed (I guess basically creating a new version that's a duplicate of an old one), and optionally to toss out data older than X versions ago.
The table's setup is fairly straightforward:
id
reference_id (string/used to determine what page the item pertains to)
content (document/html page sized amount of data)
e_user (user who changed it last)
e_timestamp (when it was changed)
I just want to have something setup to create a previous version for each edit to the content, then be able to restore to it if needed.
What's the best method for accomplishing this? Should everything be in the same table, or spread across a few different ones?
I read through a few pages on the subject, but a lot of them seemed like overkill for what i'm trying to accomplish (ex http://www.jasny.net/articles/versioning-mysql-data/ )
Are there any platforms/guides about that will help me in this endeavorer?
Ideally you would want everything in the same table with something in your query to get the correct version, however you should be careful how you do this as an inefficient query will put extra load on your server. If normally you would select a single item like this:
SELECT * FROM your_table WHERE id = 42
This would then become:
SELECT * FROM your_table
WHERE id = 42
AND date < '2010-10-12 15:23:24'
ORDER BY date DESC
LIMIT 1
Index (id, e_timestamp) to allow this to perform efficiently.
Selecting multiple rows in a single query is more tricky and requires a groupwise-maximum approach but it can be done.
You can use a technique called "auditing". You would set up audit tables. Then you would either write it into your code or setup triggers on the DB side so that every time a change is made, an entry is added into the appropriate audit table. Then you can go back through the audit table and see things like:
"Oh, yesterday Sue went in and fixed a typo"
"Uh oh, steve wiped out an entire paragraph by accident earlier today while trying to rewrite this section"
Your primary table that stores the data doesn't keep all that data, so it can stay slim. If you ever need to look at that data and say roll stuff back, you can go look in your audit table and do that. You can setup the audit table however you want, so each audit row can have the entire content BEFORE edit, and not just what was edited. That should make "rolling back" fairly easy.
Add a version column and a delete column (bool) and create some functions that compare the versions of rows with the same id. You'll definitely want to be able to easily find the current version and the previous version. To get rid of the data you'll want to write another function that sorts all of the versions of id, figures out which are old enough to be deleted, and marks them for deletion by another function. You'll probably want to have an option to make certain pages immune to deletion or postpone it.