Now that you understand how primary and foreign keys connect tables, let's explore how they create relationships between tables. Every foreign key creates a specific type of connection.

These relationship types are called "cardinality" - basically, how many records can link to each other.

Engagement Message

Have you noticed that some customers might have multiple orders, but each order belongs to just one customer?

Here's how to spot relationship types:

1:1 - Each record connects to exactly one other
1:M - Parent has many children, child has one parent
M:N - Both sides can have multiple connections

The key is asking: "How many can each side have?"

Engagement Message

Does this make sense?

Let's start with One-to-One (1:1) relationships. This means each record in Table A connects to exactly one record in Table B, and vice versa.

Think of a person and their social security number - each person has one SSN, each SSN belongs to one person.

Engagement Message

Can you think of another real-world example of a 1:1 relationship?

One-to-Many (1:M) relationships are the most common. One record in the "parent" table connects to multiple records in the "child" table.

Like our customers and orders: one customer can have many orders, but each order belongs to one customer.

Engagement Message

What's another example where one thing can have many related items?

Here's how one-to-many looks:

One customer has three orders. The foreign key appears on the "many" side.