Running total

Use a window aggregate to keep row-granularity while calculating cumulative values.

Syntax

SUM(expression) OVER (
  [PARTITION BY partition_expression, ...]
  ORDER BY sort_expression [ASC | DESC], ...
)

Example

SELECT
  month,
  revenue,
  SUM(revenue) OVER (
    ORDER BY month
  ) AS running_total
FROM monthly_revenue;

What this does

The SUM is evaluated as a window over the ordered rows, so each row keeps its own identity while also showing the cumulative total up to that point.

Common pattern

SELECT
  customer_id,
  order_date,
  amount,
  SUM(amount) OVER (
    PARTITION BY customer_id
    ORDER BY order_date
  ) AS running_customer_total
FROM orders;

Safety check before shipping

confirm the ordering is intentional and stable
decide whether a partition is desired
check whether the cumulative total should reset per group or continue across the full set