I have a database in MySQL. The values in column named Curr_BaL is updated by different operations performing on it. The application, which is written in Java, accesses that database. When it runs, by default it should retrieve the last updated value. However, I also want to be able to get the value at a specific DATE entered by the user.
I have tried to do my best, but have not successful yet, and my whole application depends on that data.
Your problem is not entirely clear. What I can understand is that you need a way to have your users aware of this "last updated" value.
You have several designs approach for this. I think that the simpler would be to fetch this value when you're authenticating your user, and set it to its session information, so it will be available at any time.
You can also have some kind of service caching this value (since I guess is the same for all users).
A very important thing you didn't mentioned is who updates this value, is an external application? is a process on the same application?.
What I can understand, users date more priority then automaticaly date. Simple way for it's using triggers. Below may be useful:
CREATE OR ALTER trigger on_table_ins for TABLE
active before insert position 0
AS
BEGIN
IF (NEW.DATEFIELD IS NULL) THEN NEW.DATEFIELDD='now';
END
It correct for firebird, so see manual for triggers and insert current date(time) for your RDBMS.
Related
I have a column Quantity in a table Inventory of MySQL which gets updated from multiple sources. I needed to maintain a track in the table on another column called QuantityLog on the last updated time of the Quantity and the source which did it. Something like this should be the content of QuantityLog column (Text type) (only the latest update details is required):
<Log>
<UpdateTime>2015-02-23 12:00:01 PM</UpdateTime>
<Source> Feeder application</Source>
</Log>
I am aware of how to do it using trigger if only the update time is required. However, with the trigger approach is there any other mechanism to get the source and use this too?
Do note pls that I am trying to perform this via triggers only as any other mechanisms of using my application to do this will require me to change in all applications that make this change and I am not inclined to do that.
There is no way MySql can know the "feeder application", unless there is a variable or table filled with that value. If you have this, it is easy to create a trigger that updates this info into the Inventory table on each change of the Quantity field.
However, if your applications use unique mysql users to connect to the database, you can of course use the CURRENT_USER() built in function inside your TRIGGER. Alternatively, CONNECTION_ID() might be helpful when tracking who did what. For example, you can create a new table that logs the connection id of your application. In that table you could write the application name, the PID and other stuff. Of course this would mean to change our application a bit by adding the appropriate insert statement after a connection is established. The overhead should be small, since usually connections are held in pools and do not get re-created all the time.
I would like to create a View that only returns new data added to the database since the last time the View was run. I know this sounds like a simple question, and there a millions of question just like it on here, but there are some restrictions in my case.
I can't use Stored Procedures, Functions or Triggers.
The user accessing the View only has read access to the database.
I posted a similar question here and was going to add an UPDATE statement to update a table with the current DateTime, and then check this table at the beginning of the View and only query after this DateTime. But the user accessing the View only has read access now.
I was also thinking there might be a type of timestamp column that updates to the current time when read with a SELECT statement, but apparently not.
Just for reference there is only ONE user accessing this view.
Any help much appreciated.
If the user only has read access to the database, then you have to store the relevant information at the application layer and not in the database. It simply is not possible to store information in the database if you don't have write access -- or at least information not part of some other process.
The recommendation would be for the application to keep track of the record returned -- keeping track of the maximum CreatedAt value or id. Then access the database using something like:
select v.*
from view v
where id > $id;
The subsequent code would update $id in the application.
I just want to send a mail when a table is populated with new row in database. My database is MySQL.
Actually i have two relation job(job_id,title,user_id) and user(user_id, user_name,email)
in MySQL
I want to send an email when new records inserted in job table
i don't know how can I'll do and my front end is in PHP.
You could possibly use a trigger to do what you want, but MySQL can't make an external call from a trigger function - only internal things (like changing another row).
I think you must default to polling the database. You might find SELECT COUNT(*) FROM table; helpful, to count the records in a table to find out if anything has changed. Most DBs run such queries very fast, so it would be ok to poll the server using it if there was only one client polling. Once you have identified a change, then use other SQL to identify whether it is a significant change (i.e. one requiring an email) and remember you might have more than one email to send :-)
I would like to ask a question for connoisseurs of SQL (MySQL, to be specific).
I have a table reservation schedules. And when a customer makes a reservation there is a time to let the client to use my service. Therefore, the reservation that he did have to leave the table reservations.
Once the time limit of use is reached, there is some method (trigger,
I believe), which automatically erase the record of this book on the
table?
If so, can someone give me some idea of how to start my search for it, or it is also totally welcome some help as some more advanced lines of code.
There is also the possibility that this only be possible to be implemented via Server-Side (PHP, ASP ...), which does not believe is so true because SQL is a language very complete (to my knowledge).
Edit1: The problem is that I believe this is a task of the DBMS, so I wanted to leave this responsibility to the MySQL The problem is: how?
A trigger is triggered by either before or after an insert , update or delete event (at least in MySQL according to the docs)
What you want is some sort of scheduled job either through your application be it php, asp.net, etc.. or cron job that calls some sort of SQL script.
So to answer, it can't be done purely with triggers.
You can use SQL jobs, but if the removal logic is to complex to manage it with queries I suggest you to use a PHP script that does all that work for you.
Just write down the data check/remove logic in PHP and set up a simple cron operation for it.
The advantage of this solution is that you can access to your scripts/classes/db providers and save your time and your can log all the operations separately (instead of logging to MySQL logs, no matter what script language you are relying on).
If you have a full control of your server the scheduled operation will look like this (if you want to check your DB entries every day at 00:01):
cat /etc/cron.d/php5
0 1 * * * php /path/to/your/script.php >> /path/to/your_script.log
..otherwise you will have to check the control panel of your hosting account and figure out how to manage
You can create one more column in your table where you will create the expiration date. Then you can on your sql server create the job that will erase all records that have expiration date less than curent date.
CREATE EVENT db_name
ON SCHEDULE EVERY 10 SECOND
DO
DELETE FROM myschema.mytable WHERE expiration_date < NOW()
I hope that will help.
I'm trying to use a simple mysql database but tweak it so that every field is backed up up to an indefinite number of versions. The best way I can illustrate this is by replacing each and every field of every table with a stack of all the values this field has ever had (each of these values should be timestamped). I guess it's kind of like having customized version control for all my data..
Any ideas on how to do this?
The usual method for "tracking any changes" to a table is to add insert/update/delete trigger procedures on the table and have those records saved in a history table.
For example, if your main data table is "ItemInfo" then you would also have an ItemInfo_History table that got a copy of the new record every time anything changed (via the triggers).
This keeps the performance of your primary table consistent, yet gives you access to the history of any changes if you need it.
Here are some examples, they are for SQL Server but they demonstrate the logic:
My Repository table
My Repository History table
My Repository Insert trigger procedure
My Repository Update trigger procedure
Hmm, what you're talking about sounds similar to Slowly Changing Dimension.
Be aware that version control on arbitrary database structures is officially a rather Hard Problem. :-)
A simple solution would be to add a version/revision field to the tables, and whenever a record is updated, instead of updating it in place, insert a copy with the changes applied and the version number incremented. Then when selecting, always choose the record with the latest version. That's roughly how most such schemes are implemented (e.g. Wikimedia does it pretty much this exact way).
Maybe a tool can help you to do that for you. Have a look at nextep designer :
https://github.com/christophefondacci/nextep-designer
With this IDE you will be able to take snapshots of your database structure and data and put it under version control. After this you can compute the differences between any 2 versions and generate the appropriate SQL that can insert / update / delete your data.
Maybe this is an alternative way to achieve what you wanted.