Running totals with SUM OVER in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to calculate a running total of sales ordered by date.

SQL

SELECT date, sales, SUM(sales) OVER (ORDER BY [1]) AS running_total FROM sales_data;

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

Aregion

Bsales

Ccustomer_id

Ddate

Attempts:

3 left

💡 Hint

Common Mistakes

Ordering by sales instead of date causes incorrect running totals.

Using a column unrelated to time order breaks the running total logic.

The running total should be ordered by the date column to accumulate sales over time.

2fill in blank

medium

Complete the code to reset the running total for each region.

SQL

SELECT region, date, sales, SUM(sales) OVER (PARTITION BY [1] ORDER BY date) AS running_total FROM sales_data;

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

Aregion

Bdate

Csales

Dcustomer_id

Attempts:

3 left

💡 Hint

Common Mistakes

Partitioning by date resets the total every day, not by region.

Not using PARTITION BY causes a running total over all data.

Partitioning by region resets the running total for each region separately.

3fill in blank

hard

Fix the error in the code to correctly calculate the running total of sales per customer ordered by date.

SQL

SELECT customer_id, date, sales, SUM(sales) OVER (PARTITION BY customer_id ORDER BY [1]) AS running_total FROM sales_data;

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

Adate

Bsales

Cregion

Dcustomer_id

Attempts:

3 left

💡 Hint

Common Mistakes

Ordering by sales causes running totals to jump incorrectly.

Ordering by customer_id inside partition by customer_id is redundant and wrong.

The running total must be ordered by date to accumulate sales chronologically per customer.

4fill in blank

hard

Fill both blanks to calculate a running total of sales per region, ordered by date, and include only sales greater than 100.

SQL

SELECT region, date, sales, SUM(sales) OVER (PARTITION BY [1] ORDER BY [2]) AS running_total FROM sales_data WHERE sales > 100;

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

Aregion

Bdate

Csales

Dcustomer_id

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping partition and order columns causes wrong grouping or ordering.

Not filtering sales before running total changes results.

Partition by region and order by date to get running totals per region over time.

5fill in blank

hard

Fill all three blanks to calculate a running total of sales per customer and region, ordered by date, including only sales in 2023.

SQL

SELECT customer_id, region, date, sales, SUM(sales) OVER (PARTITION BY [1], [2] ORDER BY [3]) AS running_total FROM sales_data WHERE EXTRACT(year FROM date) = 2023;

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

Acustomer_id

Bregion

Cdate

Dsales

Attempts:

3 left

💡 Hint

Common Mistakes

Including sales in partition or order causes errors.

Not filtering by year 2023 includes unwanted data.

Partition by customer_id and region, order by date to get running totals per customer-region over time in 2023.

Practice

1. What does the SQL expression SUM(amount) OVER (ORDER BY date) calculate?

easy

A. A running total of the amount column ordered by date

B. The total sum of amount for all rows without order

C. The average amount grouped by date

D. The maximum amount value in the table

Solution

1. Step 1: Understand SUM() with OVER()

   The SUM() function adds values, and OVER() defines how to apply it across rows.

2. Step 2: Analyze ORDER BY in OVER()

   ORDER BY date means the sum accumulates in date order, creating a running total.

3. Final Answer:

   A running total of the amount column ordered by date -> Option A

4. Quick Check:

   SUM() OVER(ORDER BY) = running total [OK]

Hint: SUM() with ORDER BY inside OVER() means running total [OK]

Common Mistakes:

• Thinking SUM() without OVER() gives running total
• Confusing running total with group total
• Ignoring ORDER BY inside OVER()

2. Which of the following is the correct syntax to calculate a running total of sales ordered by sale_date?

easy

A. SELECT sales, SUM(sales) OVER (PARTITION BY sale_date) FROM sales_table;

B. SELECT sales, SUM(sales) OVER (ORDER BY sale_date) FROM sales_table;

C. SELECT sales, SUM(sales) FROM sales_table ORDER BY sale_date;

D. SELECT sales, SUM(sales) OVER () ORDER BY sale_date FROM sales_table;

Solution

1. Step 1: Identify correct use of SUM() OVER()

   Running total requires SUM() OVER with ORDER BY clause inside OVER().

2. Step 2: Check each option's syntax

   SELECT sales, SUM(sales) OVER (ORDER BY sale_date) FROM sales_table; uses SUM(sales) OVER (ORDER BY sale_date), which is correct syntax for running total.

3. Final Answer:

   SELECT sales, SUM(sales) OVER (ORDER BY sale_date) FROM sales_table; -> Option B

4. Quick Check:

   SUM() OVER (ORDER BY ...) = running total syntax [OK]

Hint: Use SUM() OVER (ORDER BY column) for running totals [OK]

Common Mistakes:

• Using PARTITION BY instead of ORDER BY for running total
• Omitting OVER() clause
• Placing ORDER BY outside OVER()

3. Given the table sales_data with columns id, sale_date, and amount, what is the output of this query?

SELECT id, sale_date, amount, SUM(amount) OVER (ORDER BY sale_date) AS running_total FROM sales_data ORDER BY id;

Assume the data:
id | sale_date | amount
1 | 2024-01-01 | 100
2 | 2024-01-03 | 200
3 | 2024-01-02 | 150

medium

A. Running totals: 100, 350, 450 ordered by id

B. Running totals: 100, 150, 350 ordered by id

C. Running totals: 100, 450, 250 ordered by id

D. Running totals: 100, 300, 450 ordered by id

Solution

1. Step 1: Order rows by sale_date for running total

   Order by sale_date: id=1(2024-01-01), id=3(2024-01-02), id=2(2024-01-03).

2. Step 2: Calculate running total in sale_date order

   Running totals: 100 (id=1), 100+150=250 (id=3), 250+200=450 (id=2).

3. Step 3: Output ordered by id

   Order by id: id=1 (100), id=2 (450), id=3 (250).

4. Final Answer:

   Running totals: 100, 450, 250 ordered by id -> Option C

5. Quick Check:

   Running total sums in sale_date order, output sorted by id [OK]

Hint: Running total sums by ORDER BY inside OVER, output order separate [OK]

Common Mistakes:

• Assuming running total follows output ORDER BY
• Adding amounts in id order instead of sale_date order
• Confusing running total with simple sum

4. Identify the error in this query intended to calculate a running total of points ordered by game_date:

SELECT player_id, points, SUM(points) OVER (PARTITION BY player_id) ORDER BY game_date FROM game_scores;

medium

A. ORDER BY clause is outside the OVER() function

B. PARTITION BY cannot be used with SUM()

C. Missing GROUP BY clause

D. SUM() cannot be used with window functions

Solution

1. Step 1: Check placement of ORDER BY

   ORDER BY for running total must be inside OVER(), not outside the function.

2. Step 2: Understand correct syntax

   Correct syntax: SUM(points) OVER (PARTITION BY player_id ORDER BY game_date).

3. Final Answer:

   ORDER BY clause is outside the OVER() function -> Option A

4. Quick Check:

   ORDER BY must be inside OVER() for running totals [OK]

Hint: Put ORDER BY inside OVER() for running totals [OK]

Common Mistakes:

• Placing ORDER BY outside OVER()
• Confusing PARTITION BY with GROUP BY
• Thinking SUM() can't be window function

5. You have a sales table with columns region, sale_date, and amount. You want to calculate a running total of sales per region ordered by sale_date. Which query correctly achieves this?

hard

A. SELECT region, sale_date, amount, SUM(amount) OVER (ORDER BY sale_date) AS running_total FROM sales;

B. SELECT region, sale_date, amount, SUM(amount) OVER (PARTITION BY sale_date ORDER BY region) AS running_total FROM sales;

C. SELECT region, sale_date, amount, SUM(amount) FROM sales GROUP BY region, sale_date ORDER BY sale_date;

D. SELECT region, sale_date, amount, SUM(amount) OVER (PARTITION BY region ORDER BY sale_date) AS running_total FROM sales;

Solution

1. Step 1: Understand requirement for running total per region

   We need to reset running total for each region, so PARTITION BY region is required.

2. Step 2: Check ORDER BY for running total

   ORDER BY sale_date inside OVER() ensures running total accumulates by date within each region.

3. Step 3: Evaluate options

   SELECT region, sale_date, amount, SUM(amount) OVER (PARTITION BY region ORDER BY sale_date) AS running_total FROM sales; correctly uses PARTITION BY region and ORDER BY sale_date inside SUM() OVER().

4. Final Answer:

   SELECT region, sale_date, amount, SUM(amount) OVER (PARTITION BY region ORDER BY sale_date) AS running_total FROM sales; -> Option D

5. Quick Check:

   PARTITION BY region + ORDER BY sale_date = running total per region [OK]

Hint: Use PARTITION BY for groups, ORDER BY for running total order [OK]

Common Mistakes:

• Omitting PARTITION BY to separate groups
• Using GROUP BY instead of window functions
• Swapping ORDER BY columns inside OVER()