🔗 One-to-One Relationship:

• Definition: In a one-to-one relationship, each row in Table A corresponds to one (and only one) row in Table B, and vice versa.
• Sample Example: In an electronic store, consider a table products and another table product_serial_numbers. Each product in the products table has a unique serial number in the product_serial_numbers table. There would be exactly one observation for a particular product_id in both the table.

🔗 One-to-Many Relationship or Many-to-One Relationship:

• Definition: In this relationship, each row in Table A can relate to multiple rows in Table B, but a row in Table B can relate to only one row in Table A or the other way round.
• Sample Example: In our electronic store, a single customer can have multiple orders in the orders table, but each order can belong to just one customer. There is a One-to-Many relationship between the two tables.

🔗 Many-to-Many Relationship:

• Definition: Multiple records in Table A can relate to multiple records in Table B, but this relationship is typically mediated through an intermediary table.
• Example: In our electronics store database, a customer can purchase multiple products, and a product can be purchased by multiple customers. The relationship between customers and products can be represented through an intermediary table, such as orders, which contains records of each unique transaction.

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Food for Thought:

1. How would you represent product items in an order for a given order_id? Would it be a one-to-one or one-to-many relationship?
2. What would be the relationship between the product table and shipments table?

Answers:

1. It would be a one-to-many relationship: one order can have multiple product items. In our electronics database, orders table would have one-to-many relationship with orderdetails table.
2. It would be a many-to-many relationship: one product can have multiple suppliers and one supplier can ship multiple products.