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Database Constraints Explained: Primary Key, Foreign Key, Unique, Check, and Not Null
A fundamental aspect of database design is the use of constraints to maintain data integrity. This article provides an overview of five types of constraints: primary key, foreign key, unique, check, and not null.

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Source: https://dev.to/mrcaption49/types-of-constraints-primary-key-foreign-key-unique-check-and-not-null-of8