SQL
One to One and One to Many Relationships
The two simplest relationships and the single rule that decides where the foreign key goes - plus when a one to one split is actually worth it.
#Keys
Primary, foreign, candidate and surrogate keys.
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SQL
Natural vs Surrogate Keys
Should the primary key come from the data or be generated? The trade offs, the failure modes of each, and the pattern most teams settle on.
SQL
Candidate, Primary, Alternate and Composite Keys
The vocabulary of keys, explained on one table: which columns could identify a row, which one you choose, and what happens to the rest.
SQL
Referential Integrity, Cascades and Constraint Management
What happens to child rows when a parent is deleted or updated, how to choose between RESTRICT, CASCADE and SET NULL, and how to add, drop and disable...
SQL
PRIMARY KEY and FOREIGN KEY
The two constraints that give a database its structure: one that identifies a row, and one that guarantees a reference points at something real.