When an object has a one-to-many connection with one table and a many-to-many connection with another table, why do duplicate records appear when it is retrieved by its ID?

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Duplicate records may appear when an object has a one-to-many connection with one table and a many-to-many connection with another table because of the way the database is designed. When querying the database with the ID of the object, the database retrieves all the related records from both tables, resulting in duplicate records for the one-to-many connection. To avoid this, a DISTINCT keyword can be used in the query to only retrieve unique records. Additionally, the database schema can be reviewed to ensure that it is properly designed with the appropriate relationships and constraints.