It is easy to think that a database has some sort of logic, intelligence and self-awareness. It is does not.
A database is like a suitcase of clothes. Some items “go with” other items but the clothes themselves do not understand their relationship with one another. How they “go together” is intelligence outside of the suitcase.
The raw data in the database is managed externally by a Relational Database Management System and the structure of the queries. In the query below the data has to come from three different tables. The relationship of “primary key to foreign key” is un-known to SQL – you have to explain the relationship in your query (see the bold below).
SELECT
surname, brideName, groomName, itemName, description, quantity, reserved
FROM
tblCouples, tblItems, tblRegistries
WHERE
tblCouples.CoupleID = tblRegistries.CoupleID
AND tblItems.ItemID = tblRegistries.ItemID
AND reserved = TRUE
ORDER BY
surname;
In the link below you can view exactly what the inside of a database looks like. You will see that it is made up of text, delimiters, individual records and individual tables. No where is the realtionship between the tables recorded – that is why you have to code the relationship into your query.