MySQL — Default

Basic Default

CREATE TABLE users (
    id INT PRIMARY KEY,
    name VARCHAR(100),
    status VARCHAR(20) DEFAULT 'active',
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

Named Default

CREATE TABLE orders (
    id INT PRIMARY KEY,
    priority VARCHAR(10) DEFAULT 'medium' CONSTRAINT df_priority,
    quantity INT DEFAULT 1
);

Adding Default After Creation

ALTER TABLE users ALTER COLUMN status SET DEFAULT 'active';

Dropping Default

ALTER TABLE users ALTER COLUMN status DROP DEFAULT;

Default Expressions

Expression	Result
DEFAULT 'active'	Fixed string
DEFAULT CURRENT_TIMESTAMP	Current date/time
DEFAULT 0	Zero
DEFAULT NULL	NULL
DEFAULT (UUID())	Generated UUID

INSERT with DEFAULT

-- Uses the default value
INSERT INTO users (id, name) VALUES (1, 'Alice');

-- Explicitly use default
INSERT INTO users (id, name, status) VALUES (2, 'Bob', DEFAULT);

Mini Practice

Write SQL code that:

1. Creates a table with DEFAULT constraints
2. Uses CURRENT_TIMESTAMP as a default
3. Inserts a row relying on the default
4. Drops a default constraint

Up Next

Continue with Auto Increment — generating sequential numbers automatically.