How to subtract from previous row result?
问题 I need to subtract first row lot_size + substraction result from currentitems column. If no balance left then it should be 0. bal is how result column should look. rowno | location | lot_size | currentitems | bal | bal_left -------+----------+----------+--------------+--------+-------- 1 | AB1210 | 1200 | 1000 | 1000 | 200 2 | AB1220 | 1200 | 1000 | 200 | 0 3 | AB1230 | 1200 | 500 | 0 | 0 Current approach (using postgresql 9.3.1): SELECT row_number() over (ORDER BY location) as rowno,