问题
I have a database that I am trying to set up and I would like it to be in at least 3NF. However, some fields are not necessary in all situations, and the necessity of this field, not the value itself, depends on another.
In essence, I want to keep track of jobs that are on hold for one reason or another. My main table right now includes these fields:
Job No (primary Key) | Short Text | Storage Location | Coordinator
I have other tables for employee list and storage locations. Now my problem is if the job is in the storage location "LAB," then it will have an associated Lab Ticket number that I want to track. I will have another table of Lab Tickets that contains status, ECD, etc. If the storage location is "MR" then the job should have a Notification number, and a separate table will contain info about the Notifications.
Although a job can only have 1 storage location at any given time, it can move. For instance, if a job goes to "LAB" and fails the test, it will get moved to "MR" and have a Notification created.
Is it a violation of 3NF, or otherwise just bad form, to have my tblJobs have fields:
Job No (primary Key) | Short Text | Storage Location | Coordinator | Lab Ticket | Notification | ...
even if not all fields are populated or used for every job? BTW I'm using MS Access, though I don't think that matters.
Edit: I see the related posts about Null values, but my question is less about the programming (I can easily enter a non-null value [ex. "N/A"] in the not-applicable fields), and more on an abstract database design level: In short, is it bad form to have fields that may not apply to a majority of the records? I normally hate seeing a bunch of N/A fields in any table, but I'm starting think some well thought-out Queries will allow me to see only the relevant information for a specific subset. Ex. for all items in "LAB", show the lab number status.
来源：https://stackoverflow.com/questions/41966046/can-one-have-optional-fields-in-a-3nf-bcnf-database