McKinsey & Company Interview Question: What's the difference between... | Glassdoor

Interview Question

Data Analyst Interview

What's the difference between primary key and unique key

Answer

Interview Answer

3 Answers

3

Primary key may have duplicate values, unique key must have only 1 entry

Anonymous on May 23, 2017
0

There can be only one primary key, whereas there can be multiple unique keys.
Unique keys can be null

Anaonymous on Jul 10, 2017
0

Example : There's a Person table with name and document number. Name is a primary key and document number will be a unique key. Let's say that Mary is not of age for a document yet, so Mary has a null document number. Now Mary is of age and gets a document number 'x'. Sadly Mary lost her document and has to get a new document number, which can't be equal to any previous number.

Anonymous on Feb 28, 2019

Add Answers or Comments

To comment on this, Sign In or Sign Up.