An ER (Entity-Relationship) model in Oracle SQL (or any database system) is a conceptual framework used to design and represent the structure of a database. It visually defines how entities (tables) are related to each other.
Key Components of an ER Model:
Entities → Represent real-world objects (e.g., Customers, Orders, Employees). In SQL, they become tables.
Attributes → Characteristics of an entity (e.g., CustomerID, Name, Email). In SQL, they are columns.
Primary Key (PK) → A unique identifier for an entity (e.g., CustomerID).
Relationships → Define how entities are related (e.g., "A Customer places an Order"). These are represented using foreign keys in SQL.
Cardinality → Defines the type of relationship:
One-to-One (1:1) → One entity relates to only one of another.
One-to-Many (1:M) → One entity relates to multiple entities (e.g., one Customer has many Orders).
Many-to-Many (M:N) → Requires a junction table in SQL (e.g., Students and Courses).
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