NOT NULL Constraints

When creating a table, you can define a column with a NOT NULL constraint to prevent null values. This constraint ensures data integrity by guaranteeing that a column must always contain a value. If an attempt is made to insert or update a row with a null value in a NOT NULL column, the operation will be rejected, thus maintaining the integrity of the database.

Overview

MariaDB Server supports NOT NULL constraints to ensure that a column's value is not set to NULL:

When a column is declared with a NOT NULL constraint, Enterprise Server rejects operations that would write a NULL value to the column

CREATE TABLE

CREATE TABLE and NOT NULL Constraints

With MariaDB Server, the CREATE TABLE statement can be used to create a new table with a NOT NULL constraint on one or more columns:

CREATE TABLE hq_sales.invoices (
   invoice_id BIGINT UNSIGNED NOT NULL,
   branch_id INT NOT NULL,
   customer_id INT,
   invoice_date DATETIME(6),
   invoice_total DECIMAL(13, 2),
   payment_method ENUM('NONE', 'CASH', 'WIRE_TRANSFER', 'CREDIT_CARD', 'GIFT_CARD'),
   PRIMARY KEY (invoice_id)
);

ALTER TABLE

ALTER TABLE .. MODIFY COLUMN .. NOT NULL

With MariaDB Server, the ALTER TABLE statement can be used to add the NOT NULL constraint to a column using the MODIFY COLUMN clause:

ALTER TABLE hq_sales.invoices
   MODIFY COLUMN customer_id INT NOT NULL;
ALTER TABLE .. MODIFY COLUMN .. NULL

With MariaDB Server, the ALTER TABLE statement can be used to remove the NOT NULL constraint from a column using the MODIFY COLUMN clause:

ALTER TABLE hq_sales.invoices
   MODIFY COLUMN customer_id INT NULL;

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