Schema

Schema — The Blueprint

A schema is the structure of the database — the design, not the data.

Think of it as the blueprint of a building. It defines what tables exist, what columns each table has, what data types they use, and how tables relate to each other.

🧱 Example:

CREATE TABLE Users (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  email VARCHAR(100)
);

This table definition is part of the database schema.

💡 Characteristics:

• Defined once and rarely changes

• Describes the structure of data

• Stored in the system catalog

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🧠 Interview Line:

“The schema is the database’s structure, the instance is the actual data at a specific moment, and a subschema is a user-specific view of part of the schema for abstraction and access control.”