Basic SQL Interview Questions for Software Engineer

Basic-level SQL interview questions for Software Engineer positions.

1. What is normalization and why is it important?

Answer: Normalization organizes data to reduce redundancy and improve integrity. Normal forms: 1NF (atomic values), 2NF (no partial dependencies), 3NF (no transitive dependencies). Benefits: Less storage, easier updates, data consistency. Trade-off: May need JOINs for queries.

-- Unnormalized (bad)
CREATE TABLE orders (
  id INT, customer_name VARCHAR, customer_email VARCHAR,
  product_name VARCHAR, product_price DECIMAL
);

-- Normalized (good) - 3NF
CREATE TABLE customers (id INT PRIMARY KEY, name VARCHAR, email VARCHAR);
CREATE TABLE products (id INT PRIMARY KEY, name VARCHAR, price DECIMAL);
CREATE TABLE orders (
  id INT PRIMARY KEY,
  customer_id INT REFERENCES customers(id),
  product_id INT REFERENCES products(id)
);