What role does a primary key play in a database?

Question

BlackTom AI · Accepted Answer

Question: What role does a primary key play in a database?

Options:
- A) It allows duplicate values in rows
- B) It always consists of two or more attributes
- C) It defines the relationship between tables
- D) It uniquely identifies each row in a table

Analysis of each option:
Option A: It allows duplicate values in rows. This is incorrect. In a relational table, a primary key must uniquely identify each row, which means duplicate values for the primary key are not allowed. If duplicates were permitted, you could not reliably distinguish between rows that share the same key value, defeating the purpose of a primary key.

Option B: It always consists of two or more attributes. This is inaccurate. A primary key can be a single attribute (a simple primary key) or a combination of multiple attributes (a composite primary key). The key requirement is uniqueness for each row, not a fixed number of attributes.

Option C: It defines the relationship between tables. This statement is misleading. While a primary key is used in establishing relationships (via foreign keys in other tables that reference it), the primary key itself primarily serves as a unique identifier for rows within its own table. Relationships are implemented through foreign keys that reference primary keys, not by the primary key alone.

Option D: It uniquely identifies each row in a table. This is correct. The primary key's main role is to provide a unique identifier for every row, ensuring entity integrity and enabling reliable lookups, updates, and joins. The uniqueness constraint prevents duplicates and the non-null constraint (commonly applied to primary keys) ensures every row has an identifier.

What role does a primary key play in a database?

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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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