How to Use NOT NULL in SQL

The NOT NULL constraint ensures that a column cannot have NULL values. This means every row must have a valid (non-null) value for that column.

Syntax:

CREATE TABLE table_name (    column_name datatype NOT NULL,    ...);

Or add NOT NULL constraint to an existing column:

ALTER TABLE table_nameMODIFY column_name datatype NOT NULL;  -- MySQL syntax-- or in PostgreSQL:ALTER TABLE table_nameALTER COLUMN column_name SET NOT NULL;

Example 1: Create table with NOT NULL column

CREATE TABLE employees (    employee_id INT PRIMARY KEY,    name VARCHAR(100) NOT NULL,    email VARCHAR(100) NOT NULL,    department VARCHAR(50));

• Here, name and email columns must have a value for every row.

Example 2: Insert with NOT NULL columns

INSERT INTO employees (employee_id, name, email, department)VALUES (1, 'John Doe', 'john@example.com', 'Sales');

• If you try to insert NULL into name or email, SQL will give an error.

Notes:

• NOT NULL is useful to enforce required fields.

• When a column is NOT NULL, you cannot insert or update it with a NULL value.

• Some databases require NOT NULL columns to have a default value if not explicitly inserted.

If you want help adding NOT NULL constraints to existing tables or have any other questions, just ask!