Question

My question involves databases – The scenario is this:

I have an app that tracks when people borrow items. I have an existing table which tracks who they are, what they have borrowed and so on. What I would like to do is create a separate table to track what the person has borrowed, their contact info, if they returned it, etc.

My idea to do this would be to create a Dynamic table in SQL that would hold the records for 1 person, ie

John Smith
DVD; July 12, 2012; Returned in good condition; etc

As I’m still learning, I wanted to know if:

This is possible, feasible or if there is a smarter way of going about it.

Answer 1

Your answer depends on your scenario;

If you are only interested with “who” borrowed “what” (currently) and not “when” except last occurance, and you are assuming there are always only 1 copy of an item, then you can use one to one relation as:

CREATE TABLE Person
(
    PersonId        int IDENTITY(1,1)   NOT NULL,
    Name            nvarchar(30)        NOT NULL,
    Surname         nvarchar(30)        NOT NULL,
    BorrowItemId    int                 NULL FOREIGN KEY REFERENCES Item UNIQUE,
    BorrowDate      datetime            NULL,
    ReturnDate      datetime            NULL,
    ReturnCondition nvarchar(50)        NULL,
    CONSTRAINT PK_Person PRIMARY KEY CLUSTERED (PersonId ASC),
)
CREATE TABLE Item
(
    ItemId          int IDENTITY(1,1)   NOT NULL,
    ItemDescription nvarchar(50)        NOT NULL,
    CONSTRAINT [PK_Item] PRIMARY KEY CLUSTERED (ItemId ASC)
)

If you have multiple copies of each item you should remove the UNIQUE key on BorrowItemId changing relation to one to many. In case;

To see the items borrowed and returned with person information:

SELECT PersonId, Name, Surname, ItemDescription, ReturnDate, ReturnCondition
FROM Person INNER JOIN Item
    ON BorrowItemId = ItemId
WHERE BorrowItemId IS NOT NULL 
    AND ReturnDate IS NOT NULL

You can add PersonId filter in WHERE clause to query for specific person

This isn’t a good design since you can insert records without date information or you can even have records with date info but no related BorrowItemId. I suggest using many to many and keep historic data (can be handy) or overwrite using update each time the person borrows a new item