NULL in AND, OR, NOT logic in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does NULL represent in SQL?

NULL means unknown or missing value. It is not the same as zero or empty string.

beginner

What is the result of TRUE AND NULL in SQL?

The result is NULL because the unknown value could be TRUE or FALSE, so the whole expression is unknown.

beginner

What is the result of FALSE OR NULL in SQL?

The result is NULL because the unknown value might be TRUE, so the whole expression is unknown.

intermediate

What does NOT NULL evaluate to in SQL?

NOT NULL is still NULL because negation of unknown remains unknown.

intermediate

How does SQL treat NULL in logical expressions compared to TRUE or FALSE?

SQL uses three-valued logic: TRUE, FALSE, and UNKNOWN (NULL). NULL means the truth is unknown, affecting AND, OR, NOT results.

What is the result of TRUE AND NULL in SQL?

A TRUE

B Error

C FALSE

D NULL

TRUE AND NULL results in NULL because the unknown value could be TRUE or FALSE.

What is the result of FALSE OR NULL in SQL?

A TRUE

B FALSE

C NULL

D Error

FALSE OR NULL results in NULL because the unknown value might be TRUE.

What does NOT NULL evaluate to in SQL?

A FALSE

B NULL

C TRUE

D Error

NOT NULL remains NULL because negation of unknown is still unknown.

In SQL, NULL means:

A Unknown or missing value

B Empty string

C Zero

D False

NULL represents unknown or missing data, not zero or empty string.

Which logic system does SQL use for NULL values?

A Three-valued logic

B Two-valued logic

C Boolean logic only

D No logic

SQL uses three-valued logic: TRUE, FALSE, and UNKNOWN (NULL).

Explain how NULL affects the results of AND, OR, and NOT operations in SQL.

Think about how unknown values change logical outcomes.

Describe the difference between NULL and FALSE in SQL logical expressions.

Consider how SQL treats missing information.