SQL Basics

SQL Functions

SQL Joins

SQL Advanced

SQL Database

SQL Tables

SQL Constraints

SQL Performance

SQL Data Types

SQL Security

SQL NOT NULL

❮ Previous Next ❯

SQL NOT NULL Constraint

By default, a column can hold NULL values. The NOT NULL constraint enforces a column to NOT accept NULL values.

This means you cannot insert or update a record without adding a value to a NOT NULL column.

NOT NULL on CREATE TABLE

The following SQL ensures that the "ID", "LastName", and "FirstName" columns will not accept NULL values when the "Persons" table is created.

NOT NULL on CREATE TABLE

CREATE TABLE Persons (
    ID int NOT NULL,
    LastName varchar(255) NOT NULL,
    FirstName varchar(255) NOT NULL,
    Age int
);

NOT NULL on ALTER TABLE

To create a NOT NULL constraint on the "Age" column when the table is already created, use the following SQL:

NOT NULL on ALTER TABLE Example

ALTER TABLE Persons
MODIFY Age int NOT NULL;
❮ Previous Next ❯