ITPEC IP April 2022 Question 29

To enable any record in the table to be uniquely identified — the purpose of a primary key.

A primary key is a column, or a set of columns, whose value differs in every row and is never NULL. Given a key value, exactly one record is found, and other tables can point to that record with a foreign key holding the same value.

Answer (d)

Why not others:

• •(a) — whether a column takes part in arithmetic depends on its data type and meaning; being a key says nothing about it
• •(b) — any column can be searched with a condition in a query; a primary key is not needed for that (an index speeds searching, and one is usually built on the key, but that is not its purpose)
• •(c) — the opposite: the primary key is exactly what other tables reference, through foreign keys

Key rule: A primary key is unique and not NULL and identifies one row; a foreign key refers to a primary key in another table, and its values may repeat.

Databases · AI-written, may contain errors