Beginner LevelSQL & MySQL
What are Primary Keys, Foreign Keys, and Referential Integrity constraints?
❓ Interview Prompt: Explain Primary Keys, Composite Primary Keys, Foreign Keys, referential integrity constraints, and cascading actions.
Relational database integrity relies on primary and foreign key constraints:
Key Definitions:
•
Primary Key (PK): Uniquely identifies each record in a table. Must contain unique, non-null values.
•
Foreign Key (FK): A column or group of columns in one table referencing the Primary Key of another table, establishing a parent-child relationship.
•
Referential Integrity: Guarantees child FK values always reference a valid existing parent PK record ('ON DELETE CASCADE' or 'ON DELETE SET NULL').
Code Implementation Example
sql
CREATE TABLE users (
id BIGINT AUTO_INCREMENT PRIMARY KEY,
email VARCHAR(255) NOT NULL UNIQUE
);
CREATE TABLE orders (
id BIGINT AUTO_INCREMENT PRIMARY KEY,
user_id BIGINT NOT NULL,
total DECIMAL(10, 2) NOT NULL,
CONSTRAINT fk_orders_user FOREIGN KEY (user_id)
REFERENCES users(id) ON DELETE CASCADE
);💡Defining Primary Key and Foreign Key constraints with ON DELETE CASCADE.
🎯 Interview Key Takeaway
Primary Keys enforce row uniqueness; Foreign Keys enforce referential integrity across relational tables.
#SQL#Primary Key#Foreign Key#Constraints#Beginner
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