Database Design 28 - NOT NULL Foreign Key

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29 июл 2014

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Комментарии : 7

@codebreakthrough 10 лет назад

Find out more about NOT NULL Foreign Keys by watching this video! Please comment with any questions or comments! buff.ly/V4mnWo

@ishansharma4276 3 года назад

Hey Caleb, I have been following all of your databasing videos, which book would you recommend me to read and refer to whenever I am stuck the solving a relational database problem?

@wmcapunoify 8 лет назад

If you have an intermediary table for the class and instructor table, does the intermediary table would also need to define a primary key different from the foreign key from the class and instructor table or the class and instructor would be its primary key? Thank you

@vangelisdalucas2400 9 лет назад

hey Caleb thank you for your videos, they are great. Just a question over the terms "1:n relationship", "parent-child relationship" and "foreign key": if I got it right we call parent child relationship a subset of 1:n relationships in which each entity of the child table must have only one father and therefore the foreign key cannot be null. But there may be 1:n relationships in which some entities (in the "n" table) may not have a father, although if they had a father it would be only one, and therefore their foreign key may be null. Like the example in the previous video of the series where a car, after the foreign key updated, did not have an owner. is that correct ?

@codebreakthrough 9 лет назад

Vangelis Dalucas It's usually labelled as 1:M for one to many. Parent child relationship refers to a 1:m relationship, so yes. Although in some situations a 1:m relationship does NOT require the relationship to exist. Like...a car would have 1 owner and an owner can have many cars. BUT a car does not Necessarily have to have an owner if it is still being sold at the dealer... Hopefully that makes sense lol

@vangelisdalucas2400 9 лет назад

CalebTheVideoMaker2 cool, thanks a lot!