ERD: Relationship Cardinalities

[@adriannafenee7885]

Thanks, Dustin! This is exactly what I needed for today's exam. I dont know why those crows feet were giving me such a hard time but thank you for this breakdown! LOL

[@huda5450]

I have a midterm tommorow on this chapter and you honestly put together everything , it made sense, it had all the content I needed to learn. thank you so much truly. It is hard enough to find content when you are a university student and i appreciate your efforts!! :) stay blessed. 😁

[@yasmeenabdelazime769]

How it was🥺?!

[@enviousshade1770]

why do you sound like chris chan it took me a while to concentrate because of this😂😂

[@TheAbsoluteSir]

I think a game can definitely be within multiple seasons in a different year! However, within the same year, a game will only ever be in one season, like how Basketball is in winter. I feel like either answer is fine, but you have to make sure you have words between tables to help understand the relationship/

[@ekarata.361]

Wow thank you!

[@HemantaShrestha-zm7dc]

how would you describe unary many to many relationship on table , in context of referencing ?

[@Aneix12]

Very clear explanation

[@devakinandan7659]

I'd argue that players might not always need coaching and might self train as well, so it is probably optional-many. Anyways, excellent video, made me understand the concept pretty well. Thank you, justin

[@DustinOrmond]

This could definitely be a way to model this. Each database may be designed slightly different depending on the assumptions that are made.

[@devakinandan7659]

@@DustinOrmond ahh thanks mate. Reckon we got to take the ideal scenario for such cases

[@dyllgood]

Hey Dustin, thanks for the information. Just one question... On the One-to-Many (1:M) Unary Raltionship example, if the relationship cardinality was flipped, would that mean there are many managers for 1 singular person? In other words, does the relationship change based on which cardinality is on the bottom or side?

[@DustinOrmond]

No, the location of the cardinality doesn't matter in an unary relationship. The relationship is still the same.

[@dyllgood]

@@DustinOrmond So if there were multiple managers for just one person, would it become a many-to-many (M:M), because we assume the managers also manage themselves?

[@DustinOrmond]

@@dyllgood Yes, it would be many-to-many. It can be many-to-many without a manager managing themselves. The minimum (zero or one) implies whether or not they manage anyone and the maximum (one or many) implies how many people they manage. Depending on the minimum, a person may not be managed by anyone else.

[@dyllgood]

@@DustinOrmond Thank you for the help!

[@kartikkumar-xh1if]

clear explanation, thank you

[@primordialquasar8664]

Hi Dustin. What's the point of optional relationships from a database standpoint. Example: EMPLOYEE manages DEPARTMENT. An employee doesn't need to manage a department, so DEPARTMENT is optional to EMPLOYEE. But if it was wrongly identified as mandatory instead and an employee must manage a department, does that mean when an employee is created in the EMPLOYEE table, a row in the DEPARTMENT table must exist to associate the two (like some kind of dummy entry)? This is purely from a database standpoint. I just don't understand why a dummy entry needs to be created if it was wrongly identified as mandatory if it was actually in fact optional.

[@DustinOrmond]

Correct, mandatory would mean that an employee must manage a department to exist as an employee. For this reason, optional is required. However, when actually inserting data into your database, this is less of an issue because the database will always be optional many. The bigger issue is with optional one. If you use mandatory one instead of optional one then a record must be related to something when it really shouldn't. For example, if an employee optionally is associated with an order (because some orders are placed online), then the relationship must be optional one or every order would need to be associated with an employee.

[@ratminurisnaini]

Hello Dustin, I'd like to ask. If we want to connect two entities with relationship, should we have the same attributes in each entities? For example I have attribute A as a primary key in entity 1 and attribute A as a foreign key in entity 2, then I can connect these entity 1 and 2. But how if I don't have attribute A in entity 2. Can I still connect entity 1 and 2?

[@DustinOrmond]

In the ERD step, you could optionally choose to include the PK and FK in both entities. However, in my videos I don't do this until the relational model where we discuss PKs and FKs.

[@fawzisdudah8511]

The topic needs further explanation.

[@HemantaShrestha-zm7dc]

how would you describe unary many to many relationship on table , in context of referencing ?

[@DustinOrmond]

In this example, an item has many items (call a component) and each component (item) may be in many items. Therefore, we would need an associative entity because of the many to many relationship.