MySQL modified column NOT NULL error invalid use of NULL value

Scenario: MySQL adds a parent_id column to the table and sets it to not NULL, saving the Times wrong invalid use of NULL value.

Cause of error: Because the parent_id of the existing data column is null, the setting conflicts with not NULL.

Workaround: After adding the parent_id column, update the existing data parent_id to the default value, for example-1. The column's not NULL property is then modified to save successfully.

MySQL modified column NOT NULL error invalid use of NULL value