Calculate Cumulative Sum for Each Integer in Table

Q: How do I practice SQL interview questions?

PracHub provides an interactive SQL console where you can write and test queries against real database schemas. Get instant feedback and compare your solution with the expected output.

Q: What difficulty level is this coding question?

This is a medium difficulty Data Manipulation (SQL/Python) question, commonly asked during Onsite rounds at Coinbase.

Q: What role is this question designed for?

This question is commonly asked for Data Scientist candidates at Coinbase during technical interviews.

Question

numbers

+-----+
| num |
+-----+
| 1   |
| 2   |
| 13  |
| 14  |
| 15  |
+-----+

##### Scenario

You have a table containing one integer per row; for each row you must output the cumulative sum of all values that are ≤ the current row’s value.

##### Question

Write SQL that returns each number and the sum of all numbers less than or equal to it.

##### Hints

Window functions such as SUM() OVER with appropriate ordering solve this in one scan.

PracHub · Accepted Answer

This question evaluates competency in cumulative aggregation and ordering within SQL and related data-manipulation tools, focusing on calculating running totals across rows. It is commonly asked to measure practical application skills in the Data Manipulation (SQL/Python) domain, testing query formulation, efficiency and aggregation semantics at a practical application level.

Quick Overview

Calculate Cumulative Sum for Each Integer in Table