WHERE vs HAVING mental model in SQL - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to filter rows where the age is greater than 30.

SQL

SELECT * FROM employees WHERE age [1] 30;

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

A<=

B<

C=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' will select younger employees.

Using '=' will only select employees exactly 30 years old.

The WHERE clause filters rows before grouping. Here, we want employees older than 30, so we use age > 30.

2fill in blank

medium

Complete the code to show departments having more than 5 employees.

SQL

SELECT department, COUNT(*) FROM employees GROUP BY department HAVING COUNT(*) [1] 5;

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

A>

B<=

C=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using WHERE instead of HAVING to filter aggregated results.

Using '<=' will select departments with 5 or fewer employees.

The HAVING clause filters groups after aggregation. We want departments with more than 5 employees, so we use COUNT(*) > 5.

3fill in blank

hard

Fix the error in the query to filter employees with salary above 50000 after grouping by department.

SQL

SELECT department, AVG(salary) FROM employees GROUP BY department HAVING AVG(salary) [1] 50000;

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

AWHERE

B>

CHAVING

DGROUP BY

Attempts:

3 left

💡 Hint

Common Mistakes

Using WHERE to filter aggregated results causes syntax errors.

Placing HAVING before GROUP BY is incorrect.

The WHERE clause cannot filter aggregated results. Use HAVING to filter groups after aggregation.

4fill in blank

hard

Fill both blanks to filter products with price greater than 100 and groups having total quantity sold more than 50.

SQL

SELECT product_id, SUM(quantity) FROM sales WHERE price [1] 100 GROUP BY product_id HAVING SUM(quantity) [2] 50;

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

A>

B<

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' changes the filter logic.

Using WHERE instead of HAVING for aggregated filters.

WHERE filters rows before grouping (price > 100). HAVING filters groups after aggregation (SUM(quantity) > 50).

5fill in blank

hard

Fill all three blanks to select customers with age over 25, group by city, and only show cities with more than 10 customers.

SQL

SELECT city, COUNT(*) FROM customers WHERE age [1] 25 GROUP BY [2] HAVING COUNT(*) [3] 10;

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

A>

Bcity

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Using age in GROUP BY instead of city.

Using WHERE to filter aggregated counts.

Use WHERE age > 25 to filter customers before grouping. Group by city. Use HAVING COUNT(*) > 10 to filter cities with more than 10 customers.