IS NULL vs equals NULL in SQL - Quick Revision & Key Differences

Recall & Review

beginner

What does the SQL expression IS NULL check for?

It checks if a value is NULL, meaning it has no value or is unknown.

beginner

Why does the expression column = NULL not work as expected in SQL?

Because NULL means unknown, and comparing anything to unknown with = returns UNKNOWN, not TRUE.

beginner

How do you correctly check if a column has a NULL value in SQL?

Use column IS NULL to check if the column's value is NULL.

intermediate

What is the difference between IS NULL and = NULL in SQL?

IS NULL checks if a value is NULL correctly. = NULL does not work because NULL is not a value but an unknown state.

beginner

What happens if you use WHERE column = NULL in a SQL query?

The condition will never be true, so no rows with NULL values will be returned.

Which SQL condition correctly checks if a column is NULL?

A column != NULL

B column = NULL

C column IS NULL

D column <> NULL

IS NULL is the correct way to check for NULL values in SQL.

What does NULL represent in SQL?

A An unknown or missing value

B An empty string

C A zero value

D A negative number

NULL means the value is unknown or missing, not zero or empty.

If you write WHERE column = NULL, what will happen?

A It will return all rows

B It will return no rows

C It will return rows where column is NULL

D It will cause a syntax error

Comparing with = NULL always returns false or unknown, so no rows match.

How do you check if a column is NOT NULL in SQL?

A column != NULL

B column = NOT NULL

C column <> NULL

D column IS NOT NULL

IS NOT NULL is the correct way to check for values that are not NULL.

Why can't you use = NULL to compare values in SQL?

A Because NULL means unknown, and comparisons with unknown are not true

B Because NULL is a string

C Because NULL is a number

D Because SQL does not support NULL

NULL means unknown, so = NULL does not return true for any value.

Explain how to check for NULL values in SQL and why = NULL does not work.

Think about what NULL means in SQL and how comparisons behave.

Describe the difference between IS NULL and = NULL in SQL queries.

Focus on how SQL treats NULL in conditions.