SQL
NOT NULL, DEFAULT, UNIQUE and CHECK
The four constraints that guard a single table. What each one enforces, how NULL interacts with UNIQUE and CHECK, and why the database is the right pl...
Constraints
PRIMARY KEY, FOREIGN KEY, UNIQUE, NOT NULL, CHECK, DEFAULT and cascading actions.
3 notes
Notes
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.
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...