Build Running Totals With Window Functions

• Example
• Why this pattern helps
• Notes

Use this when a report needs a running total without collapsing rows.

Example

select
    customer_id,
    transaction_date,
    amount,
    sum(amount) over (
        partition by customer_id
        order by transaction_date
        rows between unbounded preceding and current row
    ) as customer_running_total
from finance.transactions;

Why this pattern helps

• keeps every transaction visible while adding cumulative context
• works well for balances, pacing, and cohort monitoring
• avoids self-joins that are harder to maintain

Notes

• include an explicit frame for predictable behavior across dialects
• add a second sort key when multiple events share the same timestamp
• remove partition by customer_id when you need a single site-wide running total