Mastering SQL WHERE Clause: Understanding NULL Values

How to Handle NULL Values in SQL WHERE Clause?

When working with SQL queries, understanding how to handle NULL values in the WHERE clause is essential for accurate data retrieval. Which of the following would be the correct syntax for a WHERE clause to return all the NULL values in the CustomerPhone column?

a) WHERE CustomerPhone=NULL

b) WHERE CustomerPhone IS NOT NULL

c) WHERE CustomerPhone IS NULL

d) WHERE CustomerPhone < NULL

Answer:

The correct syntax for a WHERE clause to return all the NULL values in the CustomerPhone column is option (c) WHERE CustomerPhone IS NULL.

When dealing with NULL values in SQL, it's important to use the proper syntax to filter out these missing values from your query results. NULL is a special marker in SQL that represents the absence of a value in a column.

The IS NULL operator is used to test for NULL values in a column. Using WHERE CustomerPhone IS NULL in your SQL query will correctly filter and return all rows where the CustomerPhone column has NULL values.

Option (a) WHERE CustomerPhone=NULL is incorrect because NULL cannot be compared using the equal operator (=). Option (b) WHERE CustomerPhone IS NOT NULL would retrieve non-NULL values. Option (d) WHERE CustomerPhone < NULL is also incorrect as NULL cannot be compared using comparison operators.

It's crucial to use the IS NULL operator when dealing with NULL values in SQL queries to ensure you get the desired results.