Searched CASE syntax in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a searched CASE expression.

SQL

SELECT CASE [1] END AS result FROM orders;

Drag options to blanks, or click blank then click option'

AWHEN amount > 100 THEN 'High'

BWHEN amount > 100 THEN 'High' ELSE 'Low'

Camount > 100

Damount

Attempts:

3 left

💡 Hint

Common Mistakes

Putting a condition directly after CASE without WHEN.

Using ELSE inside the first WHEN clause.

The searched CASE starts with CASE followed by one or more WHEN condition THEN result clauses.

2fill in blank

medium

Complete the code to add an ELSE clause to the searched CASE.

SQL

SELECT CASE WHEN score >= 90 THEN 'A' [1] END AS grade FROM students;

Drag options to blanks, or click blank then click option'

AELSE 'B'

BWHEN score < 90 THEN 'F'

CELSE 'F'

DWHEN score < 60 THEN 'F'

Attempts:

3 left

💡 Hint

Common Mistakes

Using WHEN instead of ELSE for the default case.

Omitting ELSE and expecting a default result.

The ELSE clause provides a default result if no WHEN condition matches.

3fill in blank

hard

Fix the error in the searched CASE by completing the missing WHEN clause.

SQL

SELECT CASE WHEN age < 18 THEN 'Minor' [1] END AS category FROM people;

Drag options to blanks, or click blank then click option'

AWHEN age = 18 THEN 'Adult'

BELSE 'Adult'

CWHEN age > 18 THEN 'Adult'

DWHEN age >= 18 THEN 'Adult'

Attempts:

3 left

💡 Hint

Common Mistakes

Using ELSE instead of WHEN for the adult condition.

Using incorrect comparison operators.

The searched CASE needs a WHEN clause for adults with condition age >= 18.

4fill in blank

hard

Fill both blanks to complete the searched CASE that categorizes salary.

SQL

SELECT CASE [1] THEN 'High' [2] 'Low' END AS salary_level FROM employees;

Drag options to blanks, or click blank then click option'

AWHEN salary > 5000

BWHEN salary >= 5000

CELSE

DWHEN salary < 5000

Attempts:

3 left

💡 Hint

Common Mistakes

Using WHEN instead of ELSE for the default case.

Using >= instead of > in the first condition.

The CASE starts with WHEN salary > 5000 and uses ELSE for other cases.

5fill in blank

hard

Fill both blanks to complete the searched CASE that assigns labels based on score ranges.

SQL

SELECT CASE [1] THEN 'Excellent' WHEN score >= 70 THEN 'Good' [2] 'Poor' END AS performance FROM results;

Drag options to blanks, or click blank then click option'

AWHEN score >= 90

BELSE

CWHEN score < 70

DWHEN score > 90

Attempts:

3 left

💡 Hint

Common Mistakes

Using > 90 instead of >= 90.

Omitting ELSE for the default case.

The CASE uses WHEN score >= 90 THEN 'Excellent', WHEN score >= 70 THEN 'Good', and ELSE 'Poor' for scores below 70.

Practice

1. What does the searched CASE expression in SQL do?

easy

A. Deletes rows from a table

B. Joins two tables together

C. Creates a new table

D. Returns different results based on multiple conditions

Solution

1. Step 1: Understand the purpose of searched CASE

   The searched CASE expression evaluates multiple conditions and returns a result for the first true condition.

2. Step 2: Compare with other SQL operations

   Unlike joins, deletes, or table creation, CASE is used to return values conditionally within queries.

3. Final Answer:

   Returns different results based on multiple conditions -> Option D

4. Quick Check:

   Searched CASE = conditional results [OK]

Hint: Think of CASE as SQL's if-else for conditions [OK]

Common Mistakes:

• Confusing CASE with JOIN operations
• Thinking CASE modifies tables
• Assuming CASE deletes data

2. Which of the following is the correct syntax for a searched CASE expression in SQL?

easy

A. CASE WHEN condition THEN result ELSE default END

B. CASE condition WHEN THEN result ELSE END

C. CASE THEN condition WHEN result ELSE END

D. CASE WHEN THEN condition ELSE result END

Solution

1. Step 1: Recall the searched CASE syntax

   The correct syntax starts with CASE, followed by WHEN condition THEN result, optional ELSE, and ends with END.

2. Step 2: Check each option

   Only CASE WHEN condition THEN result ELSE default END follows the correct order: CASE WHEN condition THEN result ELSE default END.

3. Final Answer:

   CASE WHEN condition THEN result ELSE default END -> Option A

4. Quick Check:

   Syntax = CASE WHEN ... THEN ... ELSE ... END [OK]

Hint: Remember: WHEN condition THEN result, ELSE optional, END last [OK]

Common Mistakes:

• Mixing order of WHEN and THEN
• Omitting END keyword
• Placing ELSE before THEN

3. Given the table Employees with column Salary, what will this query return?

SELECT Salary, CASE WHEN Salary > 5000 THEN 'High' WHEN Salary > 3000 THEN 'Medium' ELSE 'Low' END AS SalaryLevel FROM Employees;

medium

A. Returns only salaries greater than 5000

B. Shows an error because ELSE is missing

C. Labels each salary as 'High', 'Medium', or 'Low' based on value

D. Labels all salaries as 'Low'

Solution

1. Step 1: Analyze the CASE conditions

   The CASE checks if Salary > 5000, then returns 'High'; else if Salary > 3000, returns 'Medium'; otherwise 'Low'.

2. Step 2: Understand the query output

   Each row shows Salary and its label based on these conditions, so salaries are categorized correctly.

3. Final Answer:

   Labels each salary as 'High', 'Medium', or 'Low' based on value -> Option C

4. Quick Check:

   CASE categorizes salaries correctly [OK]

Hint: Read CASE conditions top to bottom, first true wins [OK]

Common Mistakes:

• Thinking ELSE is required and missing causes error
• Assuming query filters rows instead of labeling
• Ignoring order of WHEN conditions

4. Identify the error in this searched CASE expression:

SELECT Name, CASE WHEN Age > 18 THEN 'Adult' WHEN Age < 18 THEN 'Minor' END AS AgeGroup FROM People;

medium

A. Incorrect use of THEN keyword

B. No error, query is correct

C. No END keyword to close CASE

D. Missing ELSE clause for other cases

Solution

1. Step 1: Check CASE syntax completeness

   The CASE has WHEN conditions, THEN results, and ends with END keyword properly.

2. Step 2: Consider ELSE clause necessity

   ELSE is optional; if no ELSE, NULL is returned for unmatched cases, which is valid.

3. Final Answer:

   No error, query is correct -> Option B

4. Quick Check:

   ELSE optional, END required, syntax correct [OK]

Hint: ELSE is optional; END is mandatory [OK]

Common Mistakes:

• Assuming ELSE is always required
• Forgetting END keyword
• Misplacing THEN keyword

5. You want to classify products by price range using searched CASE. Which query correctly assigns 'Cheap' for prices below 50, 'Affordable' for prices between 50 and 150, and 'Expensive' for prices above 150?

hard

A. SELECT ProductName, CASE WHEN Price < 50 THEN 'Cheap' WHEN Price BETWEEN 50 AND 150 THEN 'Affordable' ELSE 'Expensive' END AS PriceRange FROM Products;

B. SELECT ProductName, CASE WHEN Price > 150 THEN 'Cheap' WHEN Price BETWEEN 50 AND 150 THEN 'Affordable' ELSE 'Expensive' END AS PriceRange FROM Products;

C. SELECT ProductName, CASE WHEN Price < 50 THEN 'Cheap' WHEN Price > 150 THEN 'Affordable' ELSE 'Expensive' END AS PriceRange FROM Products;

D. SELECT ProductName, CASE WHEN Price BETWEEN 50 AND 150 THEN 'Cheap' WHEN Price < 50 THEN 'Affordable' ELSE 'Expensive' END AS PriceRange FROM Products;

Solution

1. Step 1: Match conditions to price ranges

   Price < 50 should be 'Cheap', 50 to 150 'Affordable', above 150 'Expensive'.

2. Step 2: Verify each option's logic

   SELECT ProductName, CASE WHEN Price < 50 THEN 'Cheap' WHEN Price BETWEEN 50 AND 150 THEN 'Affordable' ELSE 'Expensive' END AS PriceRange FROM Products; correctly orders conditions and labels prices as required. Others mislabel or misorder conditions.

3. Final Answer:

   SELECT ProductName, CASE WHEN Price < 50 THEN 'Cheap' WHEN Price BETWEEN 50 AND 150 THEN 'Affordable' ELSE 'Expensive' END AS PriceRange FROM Products; -> Option A

4. Quick Check:

   Conditions match price ranges correctly [OK]

Hint: Order CASE conditions from smallest to largest range [OK]

Common Mistakes:

• Mixing condition order causing wrong labels
• Using wrong comparison operators
• Misplacing BETWEEN ranges