I'm wondering if there's a way to trigger an event into a database based on the age of the row entry. Based in a datetime field I will need to retrieve the entrys that match an exact age, but I don't want to stress the database. So I need the database to create an event in where if the field is in the database when the time comes, it will send a message or something like that.
Examples:
I have an entry that was created 23:59 hours ago. I want to trigger an event when the field reaches 24:00 hours.
I have a backend which should receive a command each time an entry becomes 1 day old.
When you INSERT the row (or otherwise set/change the time), create a one-time EVENT for 24 hours hence.
This would have to be in your application code, since "Events cannot be created, dropped or altered by another stored program, trigger or event."
Related
I want to initiate an action after 7 days from the day a specific field in my database table is updated.
I can use trigger to trigger an event on update of field in the database table. But how can I make it wait for 7 days. I was looking for scheduling an Event but that can only be scheduled for specific time. Is there any way to dynamically set the schedule time?
There are 2 ways to do it:
You store in a timestamp field when the record was last updated. You schedule a regular event to be run every couple of hours. The event's code scans the table in question and does whatever needs to be done for those records those timestamp is between the lust run of the even and the current time.
If you have lots of records you need to handle such events, then this is the recommended approach. The drawback is that timing of the event may not be fully accurate, depending on how often you schedule this event to run.
Every time you update the record you create an event specifically for that record in a trigger or stored procedure that triggers in 7 days time.
This approach gives you absolute accuracy over when an event is triggered, however, if you have a large number of changes, then this solution does not scale well.
An alternative solution could be to record the time when the change was done, but instead of event triggering base your code on user interaction. So, if the user, whose data has been updated logs on then you notify him about what you want regarding those updates that were done more than 7 days ago and the events were not seen by the user.
I am looking for a way to create a View that when queried will automatically only retrieve new records since the last query. My tables have a timestamp field for all entries, so for a simple example I can
SELECT * WHERE timestamp >= 'blah'
but I don't know how to determine what blah should be from the last query. So if the View was queried at 11:00 and then again at 12:00, the query at 12:00 should only return records added since 11:00. And so on... This all needs to be accomplished in the View, the end user should simply be able to query the View and get the results.
Is this possible?
There are two ways:
Store last access date time in database per user persistent session
table, if you have one. On next view call to database, use the
previous latest access time in the session to filter rows starting
from.
Store last access date time in user virtual session at client
environment. On every call to server, send last access date time as
well. So that server uses it to filter rows starting from.
I prefer to use second option that process won't write any data in database tables.
As there may be an unread record that slips through undetected (say it came less than a second since the last one accessed, so it has the same timestamp), set a column to auto increment (typically labelled id) and check for entries using it e.g. in PHP save the last accessed record in a $lastId variable, and use:
$sql="SELECT * WHERE `id` > '$lastId'";
I am trying to write a query to extract records updated in the last 2 hours in SQL Server 2008.
Could anyone help me write this?
select * from table where table.date1>=dateadd(hh,-2,getdate())
dateadd() function lets you subtract hours from getdate() letting you choose records updated past 2 hours
First, you have to design the table so you have a field where the time of the last change will be stored
Then, whenever you update a row, update the value in the 'last update' field. After that, you can use a script such as suggested by Vijaykumar
The downside of this method is that when a single record was changed more than once in the specified time period, you will be notified only about the time of the last update.
Another solution for tracking the updates is to read the database online transaction log file, but you'll need a third party tool for that
I'm quite new to VB and i'm working on a project to record the details of employees clocking in and clocking out. I want to know how to make it so when the 'clock in' button is clicked the time will start recording and when the 'clock out' button is pressed the time will stop recording. Also once clock out is clicked the hours in between clock in and clock out will be recorded and stored into a mySQL database.
This information will be outputted onto a DataGrid showing the time and date of when the employee has clocked in.
Then the amount of hours will be multiplied by a pre-written hourly wage .. which is already stored inside one of the tables in my mySQL database.
Any help would be appreciated.
You should store the event instead of the result.
Store the clock-in time as well as a row for the clock-out time.
Then you will need a procedure either on your database or in the application that will iterate over the rows and match clock-ins to clock-outs.
This approach will let the application crash/terminate and restart without losing data.
Alternatively you could put the clock-in and out in the same record (different columns), and just insert the clock-out into the first row that matched employee and null clock-out.
I would have the clock In button fire an event in the program that created a record for the employee ID I'm assuming you have at that time.
Then once the clock out button is clicked you would fire an event that would go out to your database and pull in the first record it found with the employee ID you are looking for, a valid clock in time and a null for the clock out time. If the program didn't find something that matched all that criteria you would have to handle that however you wanted (I would do the lookup when the employee logged in or whatever and only allow them access to the clock in button if there was no record present and only allow them to use the clock out button if there was a record found for their ID).
Once you have that record in memory you should set the clock out time and calculate the difference using the clock in time that was written to the database earlier.
I would use a stored procedure in the database to handle adding/updating/managing the record and do all the calculations and whatever else you want to do at the time of the clock in/out inside the program itself. But I think its all just preference as far as where the actual processing takes place is concerned.
The most obvious reason for this is that the program can be shut down in between clock in's and clock out's without losing anything at all. If you try to keep track of it all in memory you will lose all your clock in's once the program is shut down for whatever reason(closed manually/"End Task"ed through task manager/unhandled error).
I have a slight issue with MS-Access, which is as follows.
I have a table with a Timestamp column (the format of the field is Date/Time, the default value is Now()). The issue is that whenever I create a new record, the timestamp is set for the next record I am going to create, as opposed to the record I am creating.
This means that I create record 50, and the Timestamp is set for record 51. If I come back a week later, and create record 51, the Timestamp for record 51 will be a week out, and the timestamp will be set for record 52, which I will be creating at some point in the future.
You can re-create the problem by firing up MS-Access, creating a new table with a couple of fields, one of which is Date/Time and setting the Default Value of this field to Now().
Is this by design, or am I doing something dumb? If it is by design, how can I implement the type of Timestamp that I want (one where the Date/Time is set as the record is created) in MS-Access? If I am doing something dumb, what exactly am I doing?
Edit: Below is a screenshot of a newly created Access table:
I add some text to record one, the Timestamp gets set for record two:
I allow some time to pass, put some data into record two, and the timestamp doesn't change, and now record three has a timestamp:
If I close and open the table, the Timestamp for the (New) record gets updated to whenever I opened the table:
I allow some time to pass, update the record and the Timestamp stays at the time I opened the table:
As is already revealed in the comments, this problem comes from editing in the table with Now() set as the Default for your TimeStamp field.
I suggest you create a form instead of editing in the table. If you want it to look similar just use a datasheet form. Then on the Form's BeforeUpdate event put code in like this:
Me!TimeStamp = Now()
As a side note, I wouldn't use TimeStamp as a field name. Some RDBMS such as SQL Server have a data type called TimeStamp. It's best to avoid using field names that are data types or reserved words. Moving an Access database to SQL Server is extremely common and you could have problems when you try to do it.
Instead, I would create two fields. One called DateTimeEntered and another called DateTimeModified. I consider these two fields to be necessary in pretty much every table I make. If you ever want to do any kind of synchronization of records you'll wish you had at least a DateTimeModified field.