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!
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. 🥰🥰🥰🥰🥰
I started learning about database systems today wishing you upload more and voila, thanks for coming back!
Thanks to your normalization video I was able to finish up my first database class I thank you for the nature of your production.
All your explainer videos are masterful and second to none. Thank you!
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’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.
Hey welcome back your explanations are an absolute gem and I love your all videos.... Please keep posting
Return of the king
Thank you for your video. It was made very nice and clear.
Big fan! Keep up the good work 👍
Genius channel THANK YOU
Bro remembered his password, w vid as always
Missed your vids, hope to see more! 💛
Your back!
WOOOHOO HE'S BACK
God I love your videos thank you so much 🙏
He’s back?
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