Update current row from the results from previous row - response (2) by dnoeth

Calculate the values in an UPDATE FROM:

SELECT seq_no, num, SUM_FROM_PREV_REC,
   COALESCE(SUM(SUM_FROM_PREV_REC) 
   OVER (ORDER BY seq_no
         ROWS UNBOUNDED PRECEDING),0) +
   COALESCE(SUM(num) 
   OVER (ORDER BY seq_no
         ROWS BETWEEN UNBOUNDED PRECEDING AND 1 PRECEDING), 0)
FROM tab