Answer
A constraint is a rule applied to table columns to maintain data accuracy and consistency, such as PRIMARY KEY, UNIQUE, NOT NULL, CHECK, DEFAULT.
Quick Answer
Constraints enforce rules on data in tables. Types: PRIMARY KEY (unique + not null), FOREIGN KEY (referential integrity), UNIQUE (no duplicates), NOT NULL (required field), CHECK (custom condition on value - MySQL 8.0.16+), DEFAULT (fallback value on insert). Constraints protect data integrity at the database level, not just the application level.
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SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ