Boolean column filtering patterns in PostgreSQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Boolean column in a database?

A Boolean column stores values that can only be true or false. It helps to represent yes/no or on/off states in data.

beginner

How do you filter rows where a Boolean column is true in PostgreSQL?

Use WHERE column_name = TRUE or simply WHERE column_name to get rows where the Boolean column is true.

beginner

How do you filter rows where a Boolean column is false in PostgreSQL?

Use WHERE column_name = FALSE or WHERE NOT column_name to get rows where the Boolean column is false.

intermediate

What happens if you filter a Boolean column with WHERE column_name IS NULL?

It returns rows where the Boolean column has no value (NULL). This is different from true or false and means the value is unknown or missing.

intermediate

Why might you use WHERE column_name IS NOT TRUE instead of WHERE column_name = FALSE?

Because IS NOT TRUE includes both false and NULL values, while = FALSE only includes false. This helps catch unknown or missing data too.

Which SQL clause filters rows where a Boolean column named 'active' is true?

A WHERE active = TRUE

B WHERE active = FALSE

C WHERE active IS NULL

D WHERE active

To filter rows where 'active' is true, use WHERE active = TRUE or simply WHERE active.

How do you select rows where a Boolean column 'subscribed' is false?

A WHERE subscribed = TRUE

B WHERE subscribed IS NULL

C WHERE NOT subscribed

D WHERE subscribed = NULL

WHERE NOT subscribed filters rows where 'subscribed' is false.

What does WHERE flag IS NULL return?

A Rows where flag is true

B Rows where flag is false

C All rows

D Rows where flag has no value

IS NULL returns rows where the Boolean column has no value (NULL).

Which clause includes rows where a Boolean column is false or NULL?

A WHERE column_name IS NOT TRUE

B WHERE column_name = FALSE

C WHERE column_name = TRUE

D WHERE column_name IS NULL

IS NOT TRUE includes both false and NULL values.

What is the simplest way to filter rows where a Boolean column 'enabled' is true?

A WHERE enabled

B WHERE enabled IS NULL

C WHERE NOT enabled

D WHERE enabled = TRUE

WHERE enabled is a shorthand for WHERE enabled = TRUE.

Explain how to filter rows based on a Boolean column in PostgreSQL for true, false, and NULL values.

Think about how true, false, and unknown values are stored and checked.

Describe why you might use 'IS NOT TRUE' instead of '= FALSE' when filtering Boolean columns.

Consider how NULL values behave in Boolean filtering.