CASE in WHERE clause in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the CASE statement do inside a WHERE clause?

It allows you to apply conditional logic to decide which rows to include based on different conditions.

beginner

How do you write a simple CASE expression inside a WHERE clause?

Use WHERE CASE WHEN condition THEN value ELSE other_value END = something to filter rows based on conditions.

intermediate

Can CASE in WHERE clause return different columns or just values?

CASE returns values, not columns. It helps decide which value to compare in the WHERE filter.

intermediate

Why use CASE in WHERE instead of multiple OR conditions?

CASE can make complex conditions clearer and easier to manage by grouping logic in one expression.

beginner

Example: How to filter rows where status is 'active' if type is 1, else 'pending'?

Use WHERE (CASE WHEN type = 1 THEN status ELSE 'pending' END) = 'active' to apply this logic.

What does the CASE statement inside a WHERE clause return?

A A value to compare

B A column name

C A table

D A SQL command

CASE returns a value that the WHERE clause uses to filter rows.

Which keyword is used to start a CASE expression?

A WHEN

B ELSE

C THEN

D CASE

The CASE expression always starts with the keyword CASE.

Can you use ELSE in a CASE inside WHERE clause?

A No, ELSE is not allowed

B Yes, to provide a default value

C Only if there is one WHEN

D Only in SELECT, not WHERE

ELSE provides a default value if no WHEN condition matches.

Which is a valid use of CASE in WHERE clause?

A WHERE CASE WHEN age > 18 THEN 'adult' ELSE 'minor' END = 'adult'

B WHERE CASE age > 18 THEN 'adult' ELSE 'minor' END

C WHERE CASE age > 18 'adult' ELSE 'minor' END

D WHERE CASE age > 18 THEN 'adult' ELSE 'minor'

Option A uses correct CASE syntax with WHEN, THEN, ELSE, and END.

Why might you use CASE in a WHERE clause?

A To join tables

B To create new tables

C To apply different filters based on conditions

D To sort results

CASE in WHERE helps apply conditional filters to rows.

Explain how CASE can be used inside a WHERE clause to filter data conditionally.

Think about how CASE returns a value that the WHERE clause compares.

Write a simple example of a SQL query using CASE in the WHERE clause to filter rows based on different conditions.

Try filtering rows where a column value changes the filter condition.