Running Total Per User

Problem

Given `txns(user_id, ts, amount)`, output (user_id, ts, amount, running_total) where running_total is the cumulative sum **per user** ordered by ts.

Input

Transactions ordered by ts.

Output

user_id, ts, amount, running_total

Constraints

1 ≤ rows ≤ 10^6

Sample input

(1,'2024-01-01',10),(1,'2024-01-02',5),(2,'2024-01-01',7)

Sample output

1,2024-01-01,10,10
1,2024-01-02,5,15
2,2024-01-01,7,7

Explanation

PARTITION BY user_id resets the window per user.

window-fnrunning-sumpartition-by@Stripe

Visible test cases

in: see

out: rows

Your solution — run it, use AI if stuck

sql