HAVING clause in MySQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

MySQL

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 for aggregate filtering.

Using the wrong comparison operator like < instead of >.

The HAVING clause filters groups. Here, it selects departments with more than 5 employees, so we use >.

2fill in blank

medium

Complete the code to find products with total sales equal to 100 or more.

MySQL

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

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 for aggregate conditions.

Using <= instead of >= which filters the wrong groups.

We want products with total sales at least 100, so we use >= in HAVING.

3fill in blank

hard

Fix the error in the code to correctly filter groups with average score above 80.

MySQL

SELECT class, AVG(score) FROM results GROUP BY class HAVING AVG(score) [1] 80;

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 for aggregate filters.

Using < or <= which selects wrong groups.

The HAVING clause filters groups with average score greater than 80, so > is correct.

4fill in blank

hard

Fill both blanks to select customers with total orders more than 10 and total amount less than 500.

MySQL

SELECT customer_id, COUNT(order_id), SUM(amount) FROM orders GROUP BY customer_id HAVING COUNT(order_id) [1] 10 AND SUM(amount) [2] 500;

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

A>

B<

C<=

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up comparison operators.

Using WHERE instead of HAVING for aggregate filters.

We want customers with more than 10 orders (>) and total amount less than 500 (<).

5fill in blank

hard

Fill all three blanks to select departments with average salary above 50000, count of employees at least 5, and maximum salary below 100000.

MySQL

SELECT department, AVG(salary), COUNT(*), MAX(salary) FROM employees GROUP BY department HAVING AVG(salary) [1] 50000 AND COUNT(*) [2] 5 AND MAX(salary) [3] 100000;

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

A>

B>=

C<

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operators for the conditions.

Confusing WHERE with HAVING for aggregate filters.

The conditions are: average salary > 50000, count >= 5, and max salary < 100000.

Practice

1. What is the main purpose of the HAVING clause in SQL?

easy

A. To filter groups after aggregation

B. To filter rows before grouping

C. To sort the result set

D. To join two tables

Solution

1. Step 1: Understand filtering in SQL

   The WHERE clause filters rows before grouping, but HAVING filters after groups are formed.

2. Step 2: Identify the role of HAVING

   HAVING is used to filter groups based on aggregate conditions like COUNT or SUM.

3. Final Answer:

   To filter groups after aggregation -> Option A

4. Quick Check:

   HAVING filters groups, not rows [OK]

Hint: HAVING filters groups after aggregation, WHERE filters rows before [OK]

Common Mistakes:

• Confusing HAVING with WHERE clause
• Using HAVING without GROUP BY
• Thinking HAVING sorts data

2. Which of the following is the correct syntax to use HAVING with GROUP BY in MySQL?

easy

A. SELECT col1 FROM table HAVING COUNT(col2) > 5 GROUP BY col1;

B. SELECT col1, COUNT(col2) FROM table GROUP BY col1 HAVING COUNT(col2) > 5;

C. SELECT col1, COUNT(col2) FROM table HAVING COUNT(col2) > 5;

D. SELECT col1, COUNT(col2) FROM table GROUP BY col1 WHERE COUNT(col2) > 5;

Solution

1. Step 1: Recall correct order of clauses

   In SQL, GROUP BY comes before HAVING. The correct order is SELECT -> FROM -> GROUP BY -> HAVING.

2. Step 2: Check each option's syntax

   SELECT col1, COUNT(col2) FROM table GROUP BY col1 HAVING COUNT(col2) > 5; correctly places GROUP BY before HAVING and includes aggregate function in HAVING condition.

3. Final Answer:

   SELECT col1, COUNT(col2) FROM table GROUP BY col1 HAVING COUNT(col2) > 5; -> Option B

4. Quick Check:

   GROUP BY before HAVING [OK]

Hint: GROUP BY must come before HAVING in SQL syntax [OK]

Common Mistakes:

• Placing HAVING before GROUP BY
• Using WHERE with aggregate functions
• Omitting GROUP BY when using HAVING

3. Given the table sales with columns region and amount, what will this query return?

SELECT region, SUM(amount) AS total_sales FROM sales GROUP BY region HAVING total_sales > 1000;

medium

A. All regions with sales less than or equal to 1000

B. Syntax error because alias can't be used in HAVING

C. All regions with total sales greater than 1000

D. Empty result because HAVING filters rows

Solution

1. Step 1: Understand the query logic

   The query groups rows by region and sums amount as total_sales.

2. Step 2: Apply HAVING condition

   It filters groups where total_sales is greater than 1000. Using alias in HAVING is allowed in MySQL.

3. Final Answer:

   All regions with total sales greater than 1000 -> Option C

4. Quick Check:

   HAVING filters groups by aggregate result [OK]

Hint: HAVING filters groups by aggregate values like SUM [OK]

Common Mistakes:

• Thinking HAVING filters rows, not groups
• Assuming alias can't be used in HAVING in MySQL
• Confusing HAVING with WHERE

4. Identify the error in this query:

SELECT department, COUNT(*) FROM employees HAVING COUNT(*) > 10;

medium

A. Missing GROUP BY clause before HAVING

B. COUNT(*) cannot be used in HAVING

C. HAVING should be replaced with WHERE

D. No error, query is correct

Solution

1. Step 1: Check for GROUP BY usage

   The query uses HAVING with COUNT(*) but does not group by department. HAVING requires GROUP BY to define groups.

2. Step 2: Understand HAVING requirements

   HAVING filters groups after aggregation. Without GROUP BY, groups are not defined, causing an error.

3. Final Answer:

   Missing GROUP BY clause before HAVING -> Option A

4. Quick Check:

   HAVING needs GROUP BY to filter groups [OK]

Hint: Always use GROUP BY before HAVING to define groups [OK]

Common Mistakes:

• Using HAVING without GROUP BY
• Replacing HAVING with WHERE incorrectly
• Assuming COUNT(*) can't be in HAVING

5. You have a products table with columns category, price, and stock. Write a query to find categories where the average price is above 50 and total stock is at least 100.
Which query correctly uses HAVING to achieve this?

hard

A. SELECT category FROM products GROUP BY category WHERE AVG(price) > 50 AND SUM(stock) >= 100;

B. SELECT category FROM products HAVING AVG(price) > 50 AND SUM(stock) >= 100 GROUP BY category;

C. SELECT category FROM products WHERE AVG(price) > 50 AND SUM(stock) >= 100 GROUP BY category;

D. SELECT category FROM products GROUP BY category HAVING AVG(price) > 50 AND SUM(stock) >= 100;

Solution

1. Step 1: Recall correct clause order

   The correct order is SELECT -> FROM -> GROUP BY -> HAVING. HAVING filters groups based on aggregate conditions.

2. Step 2: Analyze each option

   SELECT category FROM products GROUP BY category HAVING AVG(price) > 50 AND SUM(stock) >= 100; correctly groups by category and uses HAVING with aggregate functions AVG(price) and SUM(stock).

3. Final Answer:

   SELECT category FROM products GROUP BY category HAVING AVG(price) > 50 AND SUM(stock) >= 100; -> Option D

4. Quick Check:

   HAVING filters grouped data with aggregate conditions [OK]

Hint: Use HAVING after GROUP BY for aggregate filters [OK]

Common Mistakes:

• Placing HAVING before GROUP BY
• Using WHERE with aggregate functions
• Omitting GROUP BY when using HAVING