ORDER BY inside OVER: does SUM accumulate?

Question

Accepted Answer

When you add ORDER BY inside OVER, the window frame defaults to 'ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW'. This means SUM accumulates from the first row up to and including the current row - a running total. Jan: 100. Feb: 100+200=300. Mar: 100+200+150=450. This is one of the most common window function patterns.