Just sticking some notes in here on this:
PRIMARY KEY constraint enforces entity integrity. It is a type of unique constraint that does not allow NULL values.
FOREIGN KEY constraint enforces referential integrity.
UNIQUE constraint guarantees that a column contains unique values in each row (can have one NULL value).
CHECK constraint enforces domain integrity.
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Lover of math. Bad at drawing.
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Thomas LaRock is an author, speaker, data expert, and SQLRockstar. He helps people connect, learn, and share. Along the way he solves data problems, too.
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