NOT NULL

What is NOT NULL?

NOT NULL means "this field must have a value". It cannot be empty.

Simple rule: Required fields use NOT NULL. Optional fields don't.

How NOT NULL Works

Basic Syntax

CREATE TABLE users (
  user_id SERIAL PRIMARY KEY,
  name VARCHAR(100) NOT NULL,
  email VARCHAR(100) NOT NULL,
  phone VARCHAR(20)
);

Example 1: Required Fields

CREATE TABLE users (
  user_id SERIAL PRIMARY KEY,
  name VARCHAR(100) NOT NULL,    -- Required
  email VARCHAR(100) NOT NULL,   -- Required
  phone VARCHAR(20)              -- Optional
);

Example 2: Insert with Required Fields

-- Works: all required fields provided
INSERT INTO users (name, email) VALUES ('John', 'john@email.com');

-- Works: phone is optional
INSERT INTO users (name, email, phone) VALUES ('Mary', 'mary@email.com', '555-0001');

Example 3: Query Users

SELECT * FROM users WHERE phone IS NULL;

NOT NULL Rules

Must have value - Cannot insert without it
Use for important fields - Name, email, dates
Skip for optional - Phone, address, notes
NULL = no value - Not zero, not empty string

Try It Below

Use the playground to practice:

SELECT * FROM users;
SELECT * FROM users WHERE phone IS NULL;

What Comes Next

Next: Learn CHECK Constraint to validate data with rules.