What do I gain by adding a timestamp column called recordversion to a table in ms-sql?
You can use that column to make sure your users don't overwrite data from another user.
Lets say user A pulls up record 1 and at the same time user B pulls up record 1. User A edits the record and saves it. 5 minutes later, User B edits the record - but doesn't know about user A's changes. When he saves his changes, you use the recordversion column in your update where clause which will prevent User B from overwriting what User A did. You could detect this invalid condition and throw some kind of data out of date error.
Nothing that I'm aware of, or that Google seems to find quickly.
You con't get anything inherent by using that name for a column. Sure, you can create a column and do the record versioning as described in the next response, but there's nothing special about the column name. You could call the column anything you want and do versioning, and you could call any column RecordVersion and nothing special would happen.
Timestamp is mainly used for replication. I have also used it successfully to determine if the data has been updated since the last feed to the client (when I needed to send a delta feed) and thus pick out only the records which have changed since then. This does require having another table that stores the values of the timestamp (in a varbinary field) at the time you run the report so you can use it compare on the next run.
If you think that timestamp is recording the date or time of the last update, it does not do that, you would need dateTime fields and constraints (To get the orginal datetime)and triggers (to update) to store that information.
Also, keep in mind if you want to keep track of your data, it's a good idea to add these four columns to every table:
CreatedBy(varchar) | CreatedOn(date) | ModifiedBy(varchar) | ModifiedOn(date)
While it doesn't give you full history, it lets you know who and when created an entry, and who and when last modified it. Those 4 columns create pretty powerful tracking abilities without any serious overhead to your DB.
Obviously, you could create a full-blown logging system that tracks every change and gives you full-blown history, but that's not the solution for the issue I think you are proposing.
Related
Sql question.
I have a customer table with:
User id, name, email, phone
The customer can update their name, email and phone at anytime on an app.
How can I find out which user id had changes in name, email or phone number on a particular date?
Since your table doesn't store the date that they made the changes, you can't.
If you add a column with a datetime type (or whatever your specific database product provides) - you could call it LastModified or something like that - then the solution becomes trivial.
I'd give you a specific example, but because you didn't tell us what database engine you use, I can't guarantee to get the syntax right.
This is an issue with RDBMSes, you cannot as they generally store say a "photograph" of your data in time not a "film" of how it got there.
Based on the RDBMS you use, you can introduce an updated_at field which will hold when the last change happened to that row either from the "UPDATE" statement (say 'UPDATE phone=000, updated_at=now() WHERE user_id=999') or set it up to autoupdate see: create column for auto-date in postgresql
I'm a pretty new programmer and I'm working on a project that I'm not sure how to make work. I'm hoping for some advice please.
Part of the project I'm working on will be used by a company to allow employees to sign up for lunch from their computers. I'm doing the project in MVC ASP.NET
The interface will look something like this:
----------------------
|1200 | Employee Dropdown Name 1
| Employee Dropdown Name 2
|---------------------
|1230 | Employee Dropdown Name 1
| Employee Dropdown Name 2
|---------------------
and on and on and on.
With this company, everything has to be recorded and stored. So, I already have a table with employee information. That will populate the drop down areas. Lunch times need to be stored in the database so it can be searched years down the line. So it has to be in a table.
The table get more tricky because not every time of the day is available for lunch (i.e. - no lunches after 0430 and before 0800).
My question is about how to create the future time slots in the database.
I could obviously make the table with all of these rows already in places for several years down the line. That's time-consuming, though, and I'll have to go back in in several years and fix it. Horrible idea.
What I'd LOVE to do is make it so every 24 hours, the database just automatically adds new rows with the next days times available - so just increment (at midnight, the program will just add the next day's times associated with that date (so at midnight on February 6, 2020, it will create February 7, 2020 0000, February 7, 2020 0030, etc. I've studied a lot but I'm still beside myself on how to make this work.
Thanks in advance everyone!!!
As I understand, you want to drive your interface from the database table so that the user can select Name 1 and Name 2 and a time slot and submit.
It sounds like you also want the available timeslots to be driven by the database also (ie, timeslot in table without names with it is availlable). This is not a good idea. As you mentioned, you would be inserting data that is not actually a record but a placeholder. That will be very confusing down the track when you come to query the data.
My approach would be to do the following:
* add NOT NULL constraints to all columns in your database (if your database supports this feature) or have your app complain very much about NULLS in any of the columns. There is no need for NULLS in your use case by the look of it.
the database should have a CHECK constraint that the time is within the allowable time range, and (assuming employees can not double book time slots) a CHECK constraint that there is no overlapping time slots, and also a UNIQUE constraint that ensures no duplicate times.... adjust to suit your needs.
your app populates times between 0800 and 1630 (8AM and 4:30PM) and also query the database for all records matching the current day so those booked slots can be removed from the list of available time slots... adjust to suit.
your app sends the user request of name and time slot to the DB. All the critical requirements are accepted or rejected by the DB schema and if there is something wrong, display an appropriate error in the app.
This way, your database is literally storing records of booked lunches.
I would NOT go down the path of pre inserting as then it becomes more complex as some records are "real" and some are artificially generated records to drive a GUI...
If you can't do the time slot calculations in your app rather than in the DB, then at least use a separate table that is maintained by a worker thread in your app OR if your DB supports it, a Stored Procedure which returns a table of available time slots.
I would use the stored procedure if I was avoiding doing complex time calculations in my app (also avoids need to worry about time zones - if you make sure to only store and display UTC times in your DB).
Having in mind structure like this:
LunchTimeSlots (id, time_slot)
Employee (id, name, preferred_time_slot_id, etc)
Lunches(employee_id, time_slot_id, date)
You need a scheduled job to add records to the "Lunches" table every midnight. How to define the job depends on your database vendor. But most of the popular rdbms have this feature. (f.e. mssql)
Despite it's possible to do what you want with db schedulers or any other scheduler, i would recommend to avoid such db design. It's always better to write real facts to the database like a list of employees or fact that lunch was served
to employee at 1pm today.
Unlike real facts, virtual data can be always generated "on-the-fly" by sql queries. F.e. by joining employees to list of dates from today till year 2100, we can get planned lunches for all employees for next 80 years.
A coworker in accounting was complaining about how she ran a query twice and it doubled her values and she got confused. Im just a Junior IT person who has very little VBA experience. I am basically just trying to add code to make it so my queries in our databases can't be run more than once unless you restart the database. I was thinking of doing a boolean check to see if a query has been run and if it has don't allow it to be run again. Or maybe I could just do a simple if statement. Please let me know if you have any input on this issue.
I couldn't find anything on the Googs either.
I would think on a date and a session ID as default values in each table, you could code the addition of both etc.
These are populated, date =date() as default value and sessionID is the DMAX from your SessionID table, as extra column in said query.
This SessionID table is incemented by a startup popup form, running macro.
The Primary Key of each table being operated on would be the date and the sessionID not allowing dupes. You probably dont need the date, just a sessionID in the PK.
It is not always the best idea to implement ad-hoc ideas by users like this.
You should analyze what happened here, and make sure it cannot happen in the application design, not by arbitrary rules.
Example: If the update query adds fees to a bill, and this must happen only once per bill, then the update query should also set a flag "fees added" in the bill record. And it should not update bills with this flag set.
I just started to use Pentaho Kettle for integration. Seems great so far, quite intuitive compared to Talend, which I was also investigating.
I am trying to migrate some customers without their keys. So I have their email addresses.
The customer may already exist in the database, so what I need to do is:
If the customer exists, add it's id to the imported field and continue.
But if the customer doesn't exist I need to get the next Hibernate key from the table Hibernate_Sequences and set it as the id.
But I don't want to always allocate a key, so I want to conditionally execute a step to allocate the next key.
So what I want to do, is in the flow execute the db procedure, which allocates the next key and returns it, only if there's no value in id from the "lookup id" step.
Is this possible?
Just posting my updated flow - so the answer was to use a filter rows component which splits the data on true/false. I really had trouble getting the id out of the database stored proc because of a bug, so I had to use decimal and then convert back to integer (which I also couldn't figure out how to do, so used a javascript component).
Yes it is. As per official documentation (i left only valuable information) "Lookup values are added as new fields onto the stream". So u need just to put step "Filter row" in Flow section and check for "id" which suppose to be added in "Existing Id Lookup" step.
I need to store an array of ints. Now my issue is, there's an operation that's done quite a few times so I'd like to limit it to one single query. In tha query, I would need to add an int to a certain int from the array.
It's for a timer of the time spent on a certain page. Currently it's just a general counter that counts for all the pages in the same field, so I only have to do
UPDATE user SET active = active+$totaltime WHERE id=:id
with the $totaltime being the time difference between last check and then. Now I'd like to store for certain pages seperately. The problem is I don't know exactly how many pages there will be. I thought about using serialize, but then I'd need to do 2 queries a lot of times which doesn't seem like a good solution.
Are there any other methods to do so?
What you need is a separate table for the levels which keeps track of active time associated with each user on each level.
Lets calls this table userlevels, and give it the following columns:
userid INT
levelid INT
active INT
The primary key should be a combination of the userid and leveid columns, since there can only be one entry for a particular combination of user and level.
Then when you want to update the amount of time a user has spent on a certain level, you would do something like:
INSERT INTO userlevels (userid,levelid,active)
VALUES (:userid,:levelid,$totaltime)
ON DUPLICATE KEY UPDATE active=active+$totaltime;
This creates a new entry in the table if the user has never been on that level before, or adds to the active time if there is already an entry.
This is mysql specific syntax, but the same thing can be achieved on other databases with different calls.