Default Values

The DEFAULT constraint in SQL is used to provide a default value for a column when no value is specified during an insert. It helps ensure that all records have valid values without requiring manual input for every column.

This is especially useful for fields like status, created_at timestamps, or boolean flags.

Syntax

CREATE TABLE table_name (
  column_name datatype DEFAULT default_value
);

To modify an existing table:

ALTER TABLE table_name
ALTER COLUMN column_name SET DEFAULT default_value;

Example: Add Default Gender to `employees`

Let’s assume most employees are male, so we set a default value for gender:

CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(50),
  age INT,
  department VARCHAR(50),
  gender VARCHAR(50) DEFAULT 'male'
);

INSERT INTO employees (id, name, age, department)
VALUES (1, 'John', 28, 'IT');

-- This will insert 'male' as gender automatically

Key Points

Default values are used when no explicit value is provided
Can apply to most data types
Helps avoid NULL values unintentionally

Syntax

Example: Add Default Gender to employees

Key Points

Example: Add Default Gender to `employees`