What is the best design for a punch in/out table?
Would you store the punch in/out in the same table or separate tables? Why?
Edit - Hourly employees punch in at the beginning of their shift and punch out at the end of their shift. Hourly - Exempt employees must punch out/in for lunch in addition to the in/out at the beginning/end of the day.
Table name: Sessions
Columns : ID, UserID, Timestamp_IN, Timestamp_OUT
Based on the info you've given, I like that simple design. There really isn't enough info though. Will the system automatically detect if it's a punch IN or OUT? Will the user specify? Etc..
It seems that you want to store a session of some sort and the time that session begins and ends. Can you punch out twice in a row without punching in? These questions are important.
Just think of it as an 'events' table, with attributes for the usual who, what (punched in or out), when and where. (How probably doesn't apply in this case.)
Been there. You want a simple events table. Don't combine punch-in and punch-out into the same record. Inevitably people will try to punch out with no punch-in record, and you can't lock up the system while you figure out why. Just record what you can and flag an administrative error.
Edit: This may be what Peter is saying. If so, upvote his - he was here first, and I have plenty of points already.
Edit: This is one of the oldest, most thoroughly debugged paradigms in existence. Go find an existing (perhaps mechanical) timeclock system and duplicate it.
assuming that your program will have PUNCH IN and PUNCH OUT buttons, then a timeclock table with user id, punch-in, and punch-out fields is a good approach
you could model this using an event table as suggested by others, but the problem with that model is that you either have to have a Type field (in or out) or you have to try to figure out if the user is punching in or out; might as well put it all in one row - that way if someone tries to punch out but never punched in, it is a trivial query to figure that out and you don't have to fool with two records and a type for each in-out pair
summary: one table with in/out dates is less storage and simpler queries
note that modeling individual clock-punch events not only requires an additional (wasteful) event-type field, it complicates processing unnecessarily, and introduces a 1:1 relationship between records that can only be found by temporal comparison
EDIT: at this point we don't really know whether the OP is using a dumb punch-clock device, or a smart punch-clock program. If the former, then there is no choice but to record punch events and reconcile later; if the latter, reconciliation/detection can occur when the punch happens.
User/In/Out is, IMO, the better option. It can easily deal with unmatched punches by using the following algorithm:
Punch In:
Punch Out:
Calculating logged time is now trivial (add up Punch Out minus Punch In for each record), as is identifying unmatched punches (look for any records where either field is null), all without needing to scan the table to try to match everything up with temporally-adjacent records every time you examine them.
Granted, there will be cases when a Punch Out may end up being associated with the wrong Punch In - but the same sequence of punches would produce the same result when using the other approach unless it uses a smarter algorithm to match them up. When users don't provide a strictly alternating In/Out/In/Out... sequence, getting them matched up correctly is purely a matter of the algorithm used to do the matching, not of the data structure used to store the punches.
As you can see from the comments, there are two distinct approaches: event-based models, where each event (whether "in" or "out") is a distinct record; and consistent in / out models, where every "in" must be followed by an "out" in the same record.
Which one is better depends on how it'll be used. Does your punch system know for sure the difference between a punch in and a punch out? Some (like card-swipe entry systems) do not. If yours doesn't, you can get into trouble with the event based system because the first time someone forgets to punch out, they've suddenly worked for 24 hours, and then they're on 16 hour days from then out. Whoops.
If they do know the difference between in and out, event-based is simpler to capture, and has less chance of interfering with human behavior (many entry card systems, like in parking garages, assume the in/out model, and they can get confused if you use one person's badge to exit and another person's to exit).
Generally, though, the simplicity you get up front results in more complexity in the algorithm to figure out what to do with the resulting punch data in cases of anomalies. If you really need it to be in in/out pairs, and you can enforce that at the front end (say, by not letting people punch in again until they punch out), then the in/out single record method will make your life on the back end much, much simpler.
I'd use a table with UserID, Date, TimeIn, TimeOut, LunchStart, and LunchEnd as fields. LunchStart and LunchEnd would be left NULL for non-hourly-exempt employees.
Some might complain about the lunch fields being always null for some employees, but this is a pretty trivial concern. This is a very simple design that ensures one record per employee per day, and makes calculating total time worked per day very easy.
Bottom line - this should be a make/buy choice, with only one real option. It's ugly, messy, ultimately user-facing, and been solved over and over and over. Please, please don't do it once again from first principles. You're going to need to buy hardware anyway, and they all come with software.
At least I hope you're not going to reinvent the hardware ...
Dear StackOverflowers,
Waves' original question on the best design for a punch in/out table was posted as a result of a brief discussion I had with him at work. We work together in the IT department at our company, and I'm the one working on a replacement for the current paper time card process. So I thought I'd throw in my oar here when waves told me that he'd posted a question on my behalf.
Currently we have a mechanical punch clock for non-exempt hourly employees that work in the plant. Non-exempt hourly OFFICE employees (the ones that wear clean shirts) fill out time sheets by hand rather than punch the clock.
My boss wants me to write a system that makes use of a proximity reader for the plant workers. This system will also allow plant as well as office workers to punch in/out using their company login IDs on a PC.
We use proximity readers at all the entrances to the building and entry/exit times are recorded in SQL Server tables using proprietary software. I have access to the SQL Server tables and have already written a companion web page that shows an In/Out Board at the receptionist's desk.
The readers at the entrances come in pairs: one on the outside of the building at each entrance and a corresponding one on the inside of each entrance. Thus the readers record whether an employee is entering or exiting the building based on the physical location of the reader.
I'm supposed to use one of those "dumb" readers as the reader for the time card replacement program. Therefore it does not know if a punch is an "in" or an "out" punch.
I've speculated that we could use two readers for punches by plant personnel in a similar fashion to using the current entry/exit readers; that is, when punching in, swipe this reader, and when punching out swipe that reader. But because of the requirement to allow any non-exempt employee to punch in/out at a PC, I've been kind of stumped as to how I'd handle the In/Out designation for office workers to match the dual readers for the plant people.
So here's what I've come up with so far:
If the In/Out key field in the Personnel table is empty/NULL, then a new record has to be inserted into the In/Out table and the InTimeStamp is filled with the TimeStamp from the "raw" table. The Personnel table's In/Out key field is then updated with the key from the newly created In/Out record.
If the In/Out key field in the Personnel table contains a key value, then the corresponding record in the In/Out table is located and updated with the latest TimeStamp from the "raw" table in the OutTimeStamp field. The In/Out key field value is then removed from the Personnel table.
It's a pretty problem, all right. Now, before you ask why we don't just use the information from the Entry/Exit system I'll tell you that because of the policies in the Human Resources dept. here, we allow people to enter the building well ahead of their shifts. BUT the employee may not punch in more than 7 minutes before the start of his shift. So the employees have been "conditioned" already to hang out at the punch clock until 7 minutes before the start of their shift; then they punch in in rapid succession.
We do this because if the employee punches in 8 minutes before the start of his shift, the company has to pay him for an extra quarter-hour. Similarly if an employee punches out at the end of his shift 8 minutes after its end, the company has to pay him for an extra quarter-hour.
I apologize for the length of this, but I felt it was important to the excellent answers that have been given here to have a fuller explanation of the context. Again, waves posted a question on my behalf and I'm essentially "hijacking" the thread. I hope his is OK.
Sincerely,
Steve Erbach
Neenah, WI
P.S., I'd like to give credit to those with helpful answers. May I do that as a "thread hijacker"?