ROLLUP for subtotals in MySQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add subtotals using ROLLUP in the GROUP BY clause.

MySQL

SELECT department, SUM(sales) FROM sales_data GROUP BY [1];

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

Adepartment WITH ROLLUP

Bdepartment ROLLUP

Cdepartment, ROLLUP

Ddepartment WITH ROLLUP()

Attempts:

3 left

💡 Hint

Common Mistakes

Using ROLLUP without WITH keyword

Adding parentheses after ROLLUP

Separating ROLLUP with a comma

In MySQL, to get subtotals using ROLLUP, you add WITH ROLLUP after the column in the GROUP BY clause.

2fill in blank

medium

Complete the code to group by two columns and include subtotals with ROLLUP.

MySQL

SELECT region, department, SUM(sales) FROM sales_data GROUP BY region, [1] WITH ROLLUP;

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

Atotal

Bregion

Csales

Ddepartment

Attempts:

3 left

💡 Hint

Common Mistakes

Using sales or total as grouping columns

Omitting the second grouping column

When grouping by multiple columns with ROLLUP, list all columns before WITH ROLLUP. Here, department is the second grouping column.

3fill in blank

hard

Fix the error in the GROUP BY clause to correctly use ROLLUP for subtotals.

MySQL

SELECT category, product, SUM(quantity) FROM inventory GROUP BY category, product [1];

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

AROLLUP

BGROUP ROLLUP

CWITH ROLLUP

DBY ROLLUP

Attempts:

3 left

💡 Hint

Common Mistakes

Using only ROLLUP without WITH

Adding GROUP or BY keywords before ROLLUP

The correct syntax to add subtotals is WITH ROLLUP after the GROUP BY columns.

4fill in blank

hard

Fill both blanks to group by year and month with subtotals using ROLLUP.

MySQL

SELECT year, [1], SUM(revenue) FROM financials GROUP BY year, [2] WITH ROLLUP;

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

Amonth

Bquarter

Dday

Attempts:

3 left

💡 Hint

Common Mistakes

Using quarter or day instead of month

Mismatching SELECT and GROUP BY columns

To group by year and month with subtotals, use month as the second column in SELECT and GROUP BY.

5fill in blank

hard

Fill all three blanks to create subtotals by country, state, and city using ROLLUP.

MySQL

SELECT [1], [2], city, SUM(population) FROM demographics GROUP BY [3], state, city WITH ROLLUP;

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

Acountry

Bstate

Dcity

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatching SELECT and GROUP BY columns

Using city in blanks where country or state is needed

The SELECT columns must match the GROUP BY columns. Here, country and state fill the blanks in SELECT and GROUP BY.

Practice

1. What does the ROLLUP keyword do in a MySQL GROUP BY query?

easy

A. It adds subtotal and total rows automatically in the grouped result.

B. It filters out NULL values from the result set.

C. It sorts the result set in descending order.

D. It creates a backup of the grouped data.

Solution

1. Step 1: Understand GROUP BY basics

   GROUP BY groups rows by column values to aggregate data.

2. Step 2: Role of ROLLUP in GROUP BY

   ROLLUP adds extra rows showing subtotals and grand totals for grouped data.

3. Final Answer:

   It adds subtotal and total rows automatically in the grouped result. -> Option A

4. Quick Check:

   ROLLUP = subtotals and totals [OK]

Hint: ROLLUP adds summary rows automatically [OK]

Common Mistakes:

• Thinking ROLLUP filters data
• Confusing ROLLUP with ORDER BY
• Assuming ROLLUP creates backups

2. Which of the following is the correct syntax to use ROLLUP in a MySQL query?

easy

A. SELECT category, SUM(amount) FROM sales GROUP BY ROLLUP(category);

B. SELECT category, SUM(amount) FROM sales ROLLUP GROUP BY category;

C. SELECT category, SUM(amount) FROM sales GROUP BY category WITH ROLLUP;

D. SELECT category, SUM(amount) FROM sales GROUP BY category ROLLUP;

Solution

1. Step 1: Recall correct ROLLUP syntax

   In MySQL, ROLLUP is used as GROUP BY ... WITH ROLLUP.

2. Step 2: Analyze each option

   SELECT category, SUM(amount) FROM sales GROUP BY category WITH ROLLUP; uses GROUP BY category WITH ROLLUP, which is correct syntax. Others misuse ROLLUP placement or syntax.

3. Final Answer:

   SELECT category, SUM(amount) FROM sales GROUP BY category WITH ROLLUP; -> Option C

4. Quick Check:

   ROLLUP goes after GROUP BY with WITH keyword [OK]

Hint: Use 'GROUP BY ... WITH ROLLUP' syntax [OK]

Common Mistakes:

• Placing ROLLUP before GROUP BY
• Using ROLLUP as a function
• Omitting WITH keyword

3. Given the table sales with columns region, product, and amount, what will be the output of this query?

SELECT region, product, SUM(amount) AS total_sales
FROM sales
GROUP BY region, product WITH ROLLUP;

medium

A. Rows grouped by region and product, plus subtotals by region and a grand total row with NULLs.

B. Only rows grouped by region and product without any subtotal or total rows.

C. Rows grouped by product only, ignoring region.

D. Syntax error due to incorrect use of ROLLUP.

Solution

1. Step 1: Understand GROUP BY with multiple columns and ROLLUP

   ROLLUP creates subtotals for each grouping level: first by region and product, then by region only, then grand total.

2. Step 2: Interpret NULL values in output

   Subtotal rows have NULL in the column(s) rolled up. The grand total row has NULL in both region and product.

3. Final Answer:

   Rows grouped by region and product, plus subtotals by region and a grand total row with NULLs. -> Option A

4. Quick Check:

   ROLLUP adds subtotal and total rows with NULL markers [OK]

Hint: ROLLUP adds subtotal rows with NULLs in rolled-up columns [OK]

Common Mistakes:

• Expecting no subtotal rows
• Confusing grouping levels
• Thinking NULL means missing data

4. You wrote this query but it gives an error:

SELECT region, product, SUM(amount) FROM sales GROUP BY region, product ROLLUP;

What is the error and how to fix it?

medium

A. ROLLUP cannot be used with multiple columns in GROUP BY.

B. GROUP BY clause must come after WHERE clause.

C. SUM() function is not allowed with ROLLUP.

D. ROLLUP must be used with the keyword WITH after GROUP BY.

Solution

1. Step 1: Identify syntax error in ROLLUP usage

   ROLLUP must be used as GROUP BY ... WITH ROLLUP, not just appended after GROUP BY columns.

2. Step 2: Correct the query syntax

   Change query to GROUP BY region, product WITH ROLLUP to fix the error.

3. Final Answer:

   ROLLUP must be used with the keyword WITH after GROUP BY. -> Option D

4. Quick Check:

   ROLLUP requires WITH keyword [OK]

Hint: Use 'WITH ROLLUP' after GROUP BY columns [OK]

Common Mistakes:

• Omitting WITH keyword
• Misplacing ROLLUP before GROUP BY
• Thinking ROLLUP disallows multiple columns

5. You want to get sales totals by region and product, plus subtotals by region and a grand total. Which query correctly uses ROLLUP and filters out only the grand total row from the result?

hard

A. SELECT region, product, SUM(amount) FROM sales GROUP BY region, product WITH ROLLUP HAVING region IS NOT NULL;

B. SELECT region, product, SUM(amount) FROM sales GROUP BY region, product WITH ROLLUP HAVING NOT (region IS NULL AND product IS NULL);

C. SELECT region, product, SUM(amount) FROM sales GROUP BY region, product WITH ROLLUP HAVING product IS NOT NULL;

D. SELECT region, product, SUM(amount) FROM sales GROUP BY region, product WITH ROLLUP HAVING region IS NULL AND product IS NULL;

Solution

1. Step 1: Understand ROLLUP output rows

   ROLLUP adds subtotal rows with NULLs in rolled-up columns; grand total row has NULL in all grouped columns.

2. Step 2: Filter out only the grand total row

   The grand total row has both region and product as NULL. To exclude it, use HAVING NOT (region IS NULL AND product IS NULL).

3. Final Answer:

   SELECT region, product, SUM(amount) FROM sales GROUP BY region, product WITH ROLLUP HAVING NOT (region IS NULL AND product IS NULL); -> Option B

4. Quick Check:

   Exclude grand total by filtering NULLs in all grouping columns [OK]

Hint: Exclude grand total by HAVING NOT all grouping columns NULL [OK]

Common Mistakes:

• Filtering only one column NULL
• Filtering to keep only grand total instead of excluding
• Using WHERE instead of HAVING with GROUP BY