A candidate key is any column, or combination of columns, that could legitimately serve as the primary key of a table. To qualify, the column set must satisfy two properties: uniqueness, meaning no two rows can ever share the same value for that set, and irreducibility (minimality), meaning you cannot remove any column from the set and still guarantee uniqueness. A table often has more than one candidate key; the designer selects one to be the primary key, and the others become alternate keys.
This distinction matters in COP4708 because key selection drives much of your schema design. The primary key you choose determines how other tables reference this one through foreign keys, while the candidate keys you do not choose still need protection so that duplicate values never slip in. In SQL, that protection comes from UNIQUE constraints, which enforce the uniqueness property of alternate keys without making them the table's identifying key.
As you watch the videos below, pay close attention to the relationship between super keys, candidate keys, and primary keys: every candidate key is a super key, but not every super key is minimal enough to be a candidate key. Try to follow the reasoning the presenters use when they test a column combination for uniqueness and then strip away unnecessary columns. Then practice that same reasoning on a sample table of your own before moving on to writing the SQL constraints.
This is a broad tour of the key types used in relational database management systems, covering primary, super, candidate, alternate, foreign, composite, and unique keys in one sitting. Based on its title and description, it defines each key type and contrasts them so you can see where candidate keys sit among the others. Expect whiteboard-style explanations with example tables illustrating each definition.
Because it treats all the key types together, it is a strong fit for the subtopic comparing candidate keys to primary keys and for seeing how alternate keys and UNIQUE constraints relate to candidate keys in practice.
This video focuses narrowly on the three concepts students most often confuse: super keys, candidate keys, and primary keys. Its description states the core idea directly, that a super key is any set of attributes that uniquely identifies a record and a candidate key is the minimal super key, with the primary key chosen from among the candidates. Expect worked examples that build super keys from a sample table and then reduce them to candidate keys.
The minimality idea is the hardest part of identifying candidate keys, and this video makes it the centerpiece, which directly supports the properties and identification subtopics.
A compact, high-level overview that sorts out primary, candidate, super, surrogate, and natural keys and explains how they differ from one another. The description notes that the goal is to clear up confusion among the many key terms used in DBMS courses. At roughly five minutes, it works well as a quick orientation or a review before an assessment.
It adds the surrogate key and natural key vocabulary to the discussion, which helps you understand why a designer might pass over a perfectly valid natural candidate key when selecting a primary key.
Together these videos build the vocabulary and reasoning MO1 requires by placing candidate keys alongside primary, foreign, composite, and surrogate keys rather than treating them in isolation. The emphasis on uniqueness and minimality, especially in the super key versus candidate key comparison, directly prepares you for MO3, where you must evaluate column combinations and identify every candidate key in a table. The treatment of surrogate and natural keys supports the judgment called for in MO4, and the coverage of unique and alternate keys sets up MO2 by showing why candidate keys you do not select still need UNIQUE constraints in your CREATE TABLE and ALTER TABLE statements. Use the module readings and hands-on SQL exercises to practice the constraint syntax and the referential actions in MO5, which these conceptual videos introduce only in passing.
These videos were chosen from YouTube on October 2, 2026. Each has captions; the player turns them on. Videos on YouTube can be changed or removed — if one no longer plays, tell your instructor. If a player does not appear, use its Watch on YouTube link.