SQL Month-over-Month Change | Dataford Interview Questions

Write a SQL query using window functions to compute each user's month-over-month change in transaction volume.

Use the users and transactions tables. Treat transaction volume as the number of transactions in each recorded calendar month, and compare each month with the user's previous recorded month.

Output

One row per user and recorded transaction month.
Columns: user_id, user_name, month_start, transaction_volume, previous_month_volume, and month_over_month_change.
For the first recorded month, previous volume and change should be NULL.
Exclude transactions that do not match a user. Order by user_id, then month_start.

Schema

users

Column	Type	Description
user_idPK	INT	Unique user identifier
user_name	VARCHAR(100)	User display name

transactions

Column	Type	Description
transaction_idPK	INT	Unique transaction identifier
user_id	INT	User associated with the transaction
transaction_date	DATE	Date on which the transaction occurred

Your question is SQL Month-over-Month Change. Start with the requirements and the two tables 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