Schema Design Best Practices | Best Practices

Introduction

Schema design is a crucial aspect of database development that influences performance, scalability, and maintainability. This tutorial covers the best practices for designing schemas in Oracle databases.

Understanding Schema Design

Schema design involves defining the structure of the database, including tables, columns, relationships, and constraints. Good schema design helps ensure data integrity, reduce redundancy, and optimize query performance.

Normalization

Normalization is the process of organizing data to minimize redundancy. There are several normal forms, each with specific rules:

1. First Normal Form (1NF)

Ensure that each table column contains atomic (indivisible) values and that each column contains values of a single type.

-- Example of a table in 1NF
CREATE TABLE students (
    student_id NUMBER PRIMARY KEY,
    student_name VARCHAR2(50),
    contact_number VARCHAR2(15)
);

2. Second Normal Form (2NF)

Ensure that the table is in 1NF and that all non-key columns are fully dependent on the primary key.

-- Example of a table in 2NF
CREATE TABLE orders (
    order_id NUMBER PRIMARY KEY,
    customer_id NUMBER,
    order_date DATE,
    FOREIGN KEY (customer_id) REFERENCES customers(customer_id)
);

3. Third Normal Form (3NF)

Ensure that the table is in 2NF and that all columns are only dependent on the primary key.

-- Example of a table in 3NF
CREATE TABLE products (
    product_id NUMBER PRIMARY KEY,
    product_name VARCHAR2(100),
    category_id NUMBER,
    FOREIGN KEY (category_id) REFERENCES categories(category_id)
);

Using Constraints

Constraints enforce rules at the database level, ensuring data integrity. Common constraints include:

1. Primary Key

Ensures that each row in a table is unique and not null.

-- Example of a primary key constraint
CREATE TABLE departments (
    department_id NUMBER PRIMARY KEY,
    department_name VARCHAR2(50) NOT NULL
);

2. Foreign Key

Ensures referential integrity by enforcing a link between the data in two tables.

-- Example of a foreign key constraint
CREATE TABLE employees (
    employee_id NUMBER PRIMARY KEY,
    employee_name VARCHAR2(100) NOT NULL,
    department_id NUMBER,
    FOREIGN KEY (department_id) REFERENCES departments(department_id)
);

3. Unique

Ensures that all values in a column are unique.

-- Example of a unique constraint
CREATE TABLE emails (
    email_id NUMBER PRIMARY KEY,
    email_address VARCHAR2(100) UNIQUE
);

4. Check

Ensures that all values in a column satisfy a specific condition.

-- Example of a check constraint
CREATE TABLE accounts (
    account_id NUMBER PRIMARY KEY,
    account_balance NUMBER CHECK (account_balance >= 0)
);

5. Not Null

Ensures that a column cannot contain null values.

-- Example of a not null constraint
CREATE TABLE users (
    user_id NUMBER PRIMARY KEY,
    username VARCHAR2(50) NOT NULL
);

Indexing

Indexes improve the speed of data retrieval operations on a table at the cost of additional space and maintenance overhead.

-- Example of creating an index
CREATE INDEX idx_employee_name ON employees (employee_name);

Partitioning

Partitioning is a database design technique that divides a large table into smaller, more manageable pieces, improving performance and manageability.

-- Example of range partitioning
CREATE TABLE sales (
    sale_id NUMBER PRIMARY KEY,
    sale_date DATE,
    amount NUMBER
)
PARTITION BY RANGE (sale_date) (
    PARTITION p1 VALUES LESS THAN (TO_DATE('01-JAN-2021', 'DD-MON-YYYY')),
    PARTITION p2 VALUES LESS THAN (TO_DATE('01-JAN-2022', 'DD-MON-YYYY')),
    PARTITION p3 VALUES LESS THAN (TO_DATE('01-JAN-2023', 'DD-MON-YYYY'))
);

Data Types

Choosing the right data types for your columns is crucial for optimizing storage and performance.

-- Example of using appropriate data types
CREATE TABLE customer_data (
    customer_id NUMBER PRIMARY KEY,
    customer_name VARCHAR2(100),
    birth_date DATE,
    email VARCHAR2(100),
    phone_number VARCHAR2(15)
);

Schema Documentation

Documenting your schema is important for maintaining and understanding the structure of your database. Use comments to describe the purpose of tables, columns, and constraints.

-- Adding comments to schema objects
COMMENT ON TABLE employees IS 'Table to store employee data';
COMMENT ON COLUMN employees.employee_id IS 'Primary key for employee table';

Conclusion

Following best practices for schema design in Oracle ensures that your database is scalable, maintainable, and performant. By understanding and applying normalization, using constraints effectively, indexing, partitioning, and documenting your schema, you can create a robust database design.

Best Practices for Schema Design in Oracle