Let’s say we want to see a report with cumulative values, for example the cumulative daily revenue at different timestamps. We want the cumulative revenue at each timestamp in the table:

`sales_ts`	`amount`
`2018-01-01 00:10:10`	`120`
`2018-01-01 00:11:00`	`100`
`2018-01-01 00:11:20`	`100`
`2018-01-01 00:12:12`	`90`
`2018-01-01 00:12:00`	`220`

select 	sales_ts,
        sum(amount) over (order by sales_ts) as cumulative
from    sales

The previous query calculates the cumulative revenue considering only the records with timestamps previous to the current timestamp.

`sales_ts`	`amount`
`2018-01-01 00:10:10`	`120`
`2018-01-01 00:11:00`	`220`
`2018-01-01 00:11:20`	`320`
`2018-01-01 00:12:00`	`540`
`2018-01-01 00:12:12`	`630`