What are constraints in SQL?

SQL keys and table design · Freshers and experienced

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Rules that protect data quality: NOT NULL, UNIQUE, PRIMARY KEY, FOREIGN KEY, CHECK (price > 0) and DEFAULT. Enforcing rules in the database means bad data is rejected no matter which application writes it.

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Keys and Table Design: Why Data Is Split Into Tables in the course SQL for Beginners: Learn Databases Step by Step.

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