Advanced ERD Concepts

Overview

• Focus on advanced ERD concepts:
  • Primary keys
  • Foreign keys
  • Bridge tables
  • Exporting ERD into database management systems (DBMS)

ERD Recap

• Previous video covered:
  • ERD entities
  • Attributes
  • Relationships
  • Cardinalities
• Current discussion continues from a simple diagram with entities: Customer, Order, Product.

Primary Keys

• Definition: Uniquely identifies every record in a table.
• Rules for Primary Keys:
  1. Unique: Identifies one record only.
  2. Never changing: Must remain constant.
  3. Never null: Cannot be left blank.
• Example of Customer Table:
  • Customer ID is chosen as the primary key because:
    • It is unique (no two customers share the same ID).
    • It never changes.
    • It is never null.

Importance of Primary Keys

• Username Example:
  • Issues changing usernames often stem from usernames being set as primary keys in databases.

Identifying Primary Keys for Other Entities

• Order Table:
  • Order Number chosen as primary key.
• Product Table:
  • Product ID chosen as primary key.
• Diagram Notation: Mark PK next to primary keys in the ERD.

Foreign Keys

• Definition: A primary key located in another entity, used to reference that record.
• Example: Customer ID in the Order entity acts as a foreign key.
• Differences from Primary Keys:
  • Foreign keys can be repeated (multiple orders by the same customer).
  • Multiple foreign keys can exist in one entity.
• Foreign Key in Order Table:
  • Customer ID and Product ID are both foreign keys in the Order entity.

Composite Primary Keys

• Definition: Two or more attributes combined to uniquely identify a record.
• Example: In a Shipment entity, product ID and order number together can form a unique identifier.
• Rules for Composite Keys:
  1. Use the fewest number of attributes.
  2. Avoid attributes that are likely to change.

Bridge Tables

• Definition: Used to create a one-to-many relationship between two entities that have a many-to-many relationship.
• Example: An Order entity serving as a bridge between Customer and Product entities.

Adding Data Types To Attributes

• Can specify data types for each attribute in the ERD (e.g., integer for Customer ID, varchar for strings).

Exporting ERD to DBMS

• Lucidchart Advantages:
  • Automatically generates code for the database from the ERD.
  • Can import existing databases and visualize them in Lucidchart.
• Process:
  • Select database type, copy code, and paste it into the DBMS to create tables accordingly.

Conclusion

• ERDs are essential for visualizing and planning databases.
• Lucidchart simplifies the ERD creation and export process.
• Next video will cover further details on building ERDs in Lucidchart.