SQL 数据库设计时间表员工与工作人员

Question

First question here so please let me know how to ask the question better if below is unhelpful.

TLDR - Should I have separates employee times tables for employees assigned to crews and those who are not?

I'm trying to design database, following 'Database Design for mere mortals' book, that tracks employees times. I'm trying to replace the weekly timesheets and crew paper sheets (with start & end times for the crew) being used. There are also individual employee weekly timesheets for those not assigned to crews. Also crew sheets sometimes have an asterisk with if someone is sick etc.

There is a relationship of Projects to crews (1:N) and for the individual employee not assigned to crews are assigned to the project. Employees are assigned to crews, normally 1:1 but headache comes when 1:N.

'Has' Relationships

So at the moment the are different types of crews say A, B, C, D, E.

Crews D & E will just fill in weekly timesheets (project, names and times, so crews D and E will both be on this same project) and the daily sheets don't include times. Sometimes like 10% of the time employees will be on both D & E on the same day.

A, B, C will have daily times on the daily sheet, but if an employee is on crew C these times take precedance over the times on sheets A or B (if they are also on A or B).

The obvious answer to have {employee, datetimestart, datetimeend} won't work as I care where the times have come from (crew, individual if exception to the crew eg sick, individual not assigned to a crew).

I can extend to have {employee, crewtype, datetimestart, datetimeend} this doesn't take care of when employee is both on D & E. I can put DE or F in this case?

Then how do I deal with those assigned to the project only? if I have {employee, crewtype, projectref, datetimestart, datetimeend} the projectref is redudant and can be derived from crewtype when this is not null. Is this a reasonable approach or would having separate tables be better?

EDIT - or should I have one table {crewid, datetimestart, datetimeend} - derive the times for employees from the crew-employee relationship, and have a separate {employee, datetimestart, datetimeend, category} with category saying if exception (eg sick) or non-assigned individual?

Answer 1

There are a lot of complicated rules in this description. If you want to create a schema that will never break these rules it will likely be a very complicated normalised schema. I would suggest that some of the rules will be best catered for in your application logic.

In terms of how you store the date, remember that you always need to cater for the exception cases, so something that happens 10% of the time, or 1% or one in a thousand still needs to be catered for, otherwise you just cant save the data.

I would tend to design for the most detailed level, which might be employee,crew,project,date,times, and possible also add an allocation column that defaults to 1, but could be 0.5 if the person is half allocated to two crews at the same time.

You could then write queries so that if a person is allocated to a crew, they get the crew time by default unless they have some overridden values, or whatever other rules you need.

Really, this is the sort of iterative modelling you would do with your business users as you tease out the design. Not always easy in a real-world scenario.

Sorry there is no definitive model here, but maybe a few tips to consider that might help along the way. Good luck with it.