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`
`2018-01-02 00:11:20`	`80`
`2018-01-02 00:11:32`	`190`
`2018-01-02 00:12:00`	`220`

select sales_ts,
sum(amount) over (partition by sales_ts order by sales_ts) 
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`
`2018-01-02 00:11:20`	`80`
`2018-01-02 00:11:32`	`270`
`2018-01-02 00:12:00`	`490`