This error commonly occurs when you try to create a foreign key that references a table that doesn't have a primary key. To resolve this problem, create a primary key on the referenced table. Then re-execute your command to create the foreign key.

How do I identify the primary key and foreign key in a table in SQL? If we want to know the table's primary keys and foreign keys. We can simply use an “information_schema. key_column_usage” view, this view will return all of the table's foreign keys and primary keys.

The main difference between a primary key vs unique key is that a primary key is a key that uniquely identifies each record in a table but cannot store NULL values. In contrast, a unique key prevents duplicate values in a column and can store NULL values.