关系数据库设计

Question

I am making an online gathering system and I am trying to design a database. I currently have four tables (Household, Household Forms, Household Members, Household Members form). Basically what I need the database to do is capture the information from the end client that fills out a form, update the information about that household, and store the previous forms. The issue I am having a difficult time wrapping my head around is regarding to the household members and its respective forms. Since I do not have control over how many individual household members will be added, I am at a lost as how to create a database that updates and archives the individual household member forms.

Here what I am considering:

HOUSEHOLD table

• UserID ( Primary Key )
• Household ID
• Head of Household
• Number of household members
• Phone Number

HOUSEHOLD FORM table

• UID ( Auto Incremented)
• Household ID (Should be same as household table)
• Head of Household
• Number of household members
• Phone Number

Right now, I have a UserID that is unique to the household. Whenever this UserID is used I know this is either the first time this household is inputting information or they are updating their information. The Household ID is what I use to form the relationship between the other tables.Both Household and household form should have the same household ID so I know that the forms are coming from that particularly household.

Additionally I need information regarding each household member.

Household Members

• UID (Auto Increments)
• Household ID (Same as Household table)
• Household Member ID
• First Name
• Last Name
• Date of Birth
• Relationship to Head of Household

Household Members Forms

• UID (Auto Increments)
• Household Members ID ( Same as household members)
• First Name
• Last Name
• Date of Birth
• Relationship to Head of Household

What I trying to do here is make the database store the individual household member information as entities in the household members table and whenever a new form is added, the household member will be updated and the previous form will saved in the household members forms. The household ID in Household members essentially tells me which household each member belongs to. The household member ID essentially lets me observe all the forms filled out from that particular individual.

Again, still really new to this and any information will be greatly appreciated!

Answer 1

It looks like your only unique information in your Household Form table is the phone number and the number of members in the household. If that is true, I would consider getting rid of that table completely.

For the phone number in the Household Form table, you should put it in the Household table because it appears to be information that belongs only to the household: it looks like there is only one per household and the number appears to be more associated with the household than any individual in the household.

I would not have a number of members in the household field at all. This number is what is known as a "derived" or "computed" value, meaning you get it from other information that is already in the database. You would use a SELECT COUNT statement along with a JOIN statement between the Household table and the Household members table. You can find lots of information on these SQL statements for whichever database you use with a Google search.

I would also delete the Household Members Forms table. It appears to be just a subset of the Household Members table.

I think what you were trying to accomplish with the Household Members Forms table and the Household Form table was to relate the Household and the Household Member table. When you use a table to do this, it is called a join table, but you usually only use join tables for "many-to-many" relationships. In your case, a many-to-many relationship would be where a house can have many members in it AND where an individual can belong to several households.

It looks like you are trying to model a "has many/belongs to" relationship. In your case, that would be where a single household can have several members in it but any individual only ever belongs to one household. To link or relate the data in this relationship, all you need is to place a foreign key in the belongs to table. In your case, the belongs to table is the Household Members table and the foreign key would be the Household ID.