How many primary keys can a table have?

Question

BlackTom AI · Accepted Answer

Consider the concept of a primary key in a relational table. 
Option 1: One. A table can have exactly one primary key constraint, though that key can be a single column or a composite key made up of multiple columns. This is the standard rule in relational databases. 
Option 2: Zero. While some tables might be created without an explicitly defined primary key, the question asks how many primary keys a table can have; having zero primary keys would violate the typical design expectation that each row should have a unique identifier. In practice, you may encounter tables without a primary key, but that does not mean zero is the allowed count when counting primary key constraints per table. 
Option 3: As many as necessary. This is incorrect because a table cannot have more than one primary key constraint; there is a single designated primary key per table, even if that key spans multiple columns. 
Option 4: Two. This contradicts the rule that only one primary key constraint is permitted per table, regardless of the number of columns it contains. 
In summary, the correct understanding is that a table has exactly one primary key constraint (though it can be composed of multiple columns), while the other options misstate the constraints or flexibility around primary keys.

How many primary keys can a table have?

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Question at position 11 In ERDs, the primary key isAn attribute that cannot be modified after it is setAn attribute that uniquely identifies each record in a database tableA graphical symbol indicating the connection between entitiesA set of optional attributes linked to an entity

A database table usually has a(n) _______________________ that uniquely identifies each row in the table.

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