Question

How would you retrieve data on all the customers where no phone number is stored?

a) SELECT * FROM customers WHERE phone IS NULL;
b) SELECT * FROM customers WHERE phone = '';
c) SELECT * FROM customers WHERE phone = 'N/A';
d) SELECT * FROM customers WHERE phone = 0;

Answer 1

The correct SQL query to retrieve data on all customers with no phone number stored is SELECT * FROM customers WHERE phone IS NULL; since NULL represents the absence of a value in SQL.

Step-by-step explanation:

When retrieving data from a database, we must use SQL (Structured Query Language), which is a specialized language designed for managing data held in a relational database management system. To find all the customers where there is no phone number stored, we need to check for NULL values in the phone column. The correct SQL query to accomplish this would be:

SELECT * FROM customers WHERE phone IS NULL;

This is because NULL in SQL represents the absence of a value, meaning that the field is left blank or uninitialized. Option a) is thus the correct choice. Comparatively, option b) checks for an empty string, option c) for a specific string 'N/A', and option d) for the numeric value 0. These are different from a NULL value and would not correctly identify customers without a phone number unless the database was specifically designed to store missing phone numbers in such a manner.