CORRECTIONS: Expand this comment to see corrections. CONTENTS 0:00 Introduction 0:57 Extracting information requirements 2:58 Relationships 4:07 Cardinality 6:42 Basics of Chen notation 9:50 Attributes 11:04 Weak entities 13:17 Crow's foot notation 15:10 M-M / 1-M / 1-1 relationships 18:07 From ERD to relational database 20:00 Conclusion * CORRECTIONS * In the part of the video dealing with "weak entities", at 12:06, I've underlined the Line Sequence Number attribute with a solid line. By convention, an attribute like Line Sequence Number (i.e. the attribute that, in combination with its parent's unique identifier, identifies the weak entity) should actually be underlined with a dotted line.
Before the we started our current project, I forced our desinger to watch your videos. He now drafts the DB himself and does not make up strange relations anymore hence I only have to improve on the draft. You safed me a ton of work. Thank you!
Thanks Decomplexify, your videos have been really clear, easy to understand and have appropriate visuals. Please. upload more content related to database. 😃🙏
Are you kidding me? This took my lecturer 6 months and I could not comprehend WTF he was talking about.. Bro explained normalizations without even mentioning it LOL Thank You!
How do we draw "Views" or query results? Suppose I'm developing a pet app that has a page where I list all my pets. What does it look like to represent that query in a diagram? I find that apps are just a bunch of queries with UI. I also spend too long over thinking the perfect DB schema for all scenarios, but ultimately it's just a list view, details view, etc. How do we represent those in a diagram that helps developing the DB schema I actually need? I hope I'm making sense. s/o from 🇿🇼 🇿🇼 🇿🇼 keep up the good work
Greetings, and thanks for the question. All you really need to do is write down, in words, what you want the user to see. You mention "a page where I list all my pets": this is fine but the next step is to be a little bit more specific about the nature of this list of pets - for example, perhaps what you really want is "a page where I list the name, address, and pet type [e.g. Dog, Cat, or Hamster] of each pet." Now circle the nouns that appeared in that sentence. They are "pet", "name" [i.e. name of the pet], "address", and "pet type". On your ERD, draw a box to represent each of those nouns. A "Pet" box, an "Address" box, a "Pet Type" box ... and rather than doing a "Name" box I would likely just recognize that Pet Name is going to be an attribute of "Pet". Then think about the real-life relationships among Pets, Pet Types, and Addresses, and draw them in. You can then proceed to write down, in words, descriptions of what needs to appear on some of the other pages. For example, your "pet details" page (which might just involve all the same nouns you already incorporated into the ERD, in which you've got nothing extra to add to the diagram - or it might include some extra stuff as well, in which case you've got some more boxes / relationships to draw on the diagram). So, basically the procedure outlined in the video.
That's a little complicated. On most database platforms, you'll need to write "triggers", for example a trigger to ensure that if an attempt is made to put through a transaction that deletes the only remaining person associated with a given address, this attempt is detected and the transaction is automatically rolled back. If you are designing your database using a sophisticated data modelling tool like ERwin, the tool will be able to see (from the cardinalities you specified on the relationship in your diagram) that these triggers are needed, and will script them for you automatically.
CORRECTIONS: Expand this comment to see corrections.
CONTENTS
0:00 Introduction
0:57 Extracting information requirements
2:58 Relationships
4:07 Cardinality
6:42 Basics of Chen notation
9:50 Attributes
11:04 Weak entities
13:17 Crow's foot notation
15:10 M-M / 1-M / 1-1 relationships
18:07 From ERD to relational database
20:00 Conclusion
* CORRECTIONS *
In the part of the video dealing with "weak entities", at 12:06, I've underlined the Line Sequence Number attribute with a solid line. By convention, an attribute like Line Sequence Number (i.e. the attribute that, in combination with its parent's unique identifier, identifies the weak entity) should actually be underlined with a dotted line.
I HAVE MISSED YOU SO MUCH.WELCOME BACK. 🥰🥰🥰🥰🥰
Before the we started our current project, I forced our desinger to watch your videos. He now drafts the DB himself and does not make up strange relations anymore hence I only have to improve on the draft. You safed me a ton of work. Thank you!
You're welcome! Glad I've been able to help your designer to do things better.
I started learning about database systems today wishing you upload more and voila, thanks for coming back!
I’m just want to let you know you helped me get started as a master data manager, I’ve since been promoted to Sr analyst thank you so much.
Congratulations! That's amazing, and you are welcome - it's really gratifying to learn that my videos have played some part in this.
Thanks to your normalization video I was able to finish up my first database class I thank you for the nature of your production.
Those normalisation vids are 🔥 🔥 🔥
All your explainer videos are masterful and second to none. Thank you!
Thanks Decomplexify, your videos have been really clear, easy to understand and have appropriate visuals.
Please. upload more content related to database. 😃🙏
Thanks, these videos are an invaluable resource!
Return of the king
the man, the myth, the legend. welcome back bro
Tomorrow i was thinking of revising students about ER diagram, what a perfecting timing of this video recommendation ❤
Hey welcome back your explanations are an absolute gem and I love your all videos.... Please keep posting
Are you kidding me? This took my lecturer 6 months and I could not comprehend WTF he was talking about.. Bro explained normalizations without even mentioning it LOL Thank You!
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Thank you for this!
کارت درسته به انتشار ویدیوهات ادامه بده :) ❤
Big fan! Keep up the good work 👍
Thank you for your video. It was made very nice and clear.
Missed your vids, hope to see more! 💛
Thanks.. best explainer
Genius channel THANK YOU
WOOOHOO HE'S BACK
Prima. thanks for the video
welcome back
Bro remembered his password, w vid as always
Your back!
God I love your videos thank you so much 🙏
Kindly bring video on Stored procedures.
He’s back?
AMAZING
How do we draw "Views" or query results?
Suppose I'm developing a pet app that has a page where I list all my pets. What does it look like to represent that query in a diagram?
I find that apps are just a bunch of queries with UI. I also spend too long over thinking the perfect DB schema for all scenarios, but ultimately it's just a list view, details view, etc. How do we represent those in a diagram that helps developing the DB schema I actually need?
I hope I'm making sense.
s/o from 🇿🇼 🇿🇼 🇿🇼 keep up the good work
Greetings, and thanks for the question. All you really need to do is write down, in words, what you want the user to see. You mention "a page where I list all my pets": this is fine but the next step is to be a little bit more specific about the nature of this list of pets - for example, perhaps what you really want is "a page where I list the name, address, and pet type [e.g. Dog, Cat, or Hamster] of each pet."
Now circle the nouns that appeared in that sentence. They are "pet", "name" [i.e. name of the pet], "address", and "pet type".
On your ERD, draw a box to represent each of those nouns. A "Pet" box, an "Address" box, a "Pet Type" box ... and rather than doing a "Name" box I would likely just recognize that Pet Name is going to be an attribute of "Pet".
Then think about the real-life relationships among Pets, Pet Types, and Addresses, and draw them in.
You can then proceed to write down, in words, descriptions of what needs to appear on some of the other pages. For example, your "pet details" page (which might just involve all the same nouns you already incorporated into the ERD, in which you've got nothing extra to add to the diagram - or it might include some extra stuff as well, in which case you've got some more boxes / relationships to draw on the diagram).
So, basically the procedure outlined in the video.
How would you enforce a one to many relationship in the other direction in SQL? Ex. enforce that every Address is associated with at least one Person.
That's a little complicated. On most database platforms, you'll need to write "triggers", for example a trigger to ensure that if an attempt is made to put through a transaction that deletes the only remaining person associated with a given address, this attempt is detected and the transaction is automatically rolled back.
If you are designing your database using a sophisticated data modelling tool like ERwin, the tool will be able to see (from the cardinalities you specified on the relationship in your diagram) that these triggers are needed, and will script them for you automatically.
omg