Per-Customer Cumulative Sales | Dataford Interview Questions

SQL: given (Cust_Id, Prod, Sales), output per-customer cumulative sales (window cumulative sum). Asked in the Round 1 stage. Write a PostgreSQL query using the customer_sales table.

Output

One row per source record with columns cust_id, prod, sales, and cumulative_sales.
cumulative_sales must accumulate sales separately for each customer, ordered by prod ascending. Include rows with NULL sales.
Sort the final result by cust_id ascending, then prod ascending with NULL products last.

Schema

customer_sales

Column	Type	Description
cust_id	INT	Customer identifier
prod	VARCHAR(100)	Product name used for ordering
sales	NUMERIC(12,2)	Sales amount for the customer and product

Your question is Per-Customer Cumulative Sales. Start with the requirements and the one table in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

Problem

SQL: given (Cust_Id, Prod, Sales), output per-customer cumulative sales (window cumulative sum). Asked in the Round 1 stage. Write a PostgreSQL query using the customer_sales table.

Output

One row per source record with columns cust_id, prod, sales, and cumulative_sales.
cumulative_sales must accumulate sales separately for each customer, ordered by prod ascending. Include rows with NULL sales.
Sort the final result by cust_id ascending, then prod ascending with NULL products last.

Schema

customer_sales

Column	Type	Description
cust_id	INT	Customer identifier
prod	VARCHAR(100)	Product name used for ordering
sales	NUMERIC(12,2)	Sales amount for the customer and product

Your question is Per-Customer Cumulative Sales. Start with the requirements and the one table in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.