在sql server表中计算列总和

Question

I have try to record numbers on to a db, but I can't insert column sum. Example:

Records:

check1      check2      check3       sum_number        roll_sum
  500         510         500           3.3               3.3(should be)
  490         500         505          -1.6               1.7 (should be)

But my roll sum's always is NULL.

My PHP script is

($sum_number + (SELECT SUM(roll_sum) FROM table_name))

But, if I manually put first number to roll_sum than script counting another rows fine. How do I make script work fine?

Answer 1

Try this:

SELECT SUM(Case ROLL_SUM WHEN NULL THEN SUM_NUMBER ELSE ROLL_SUM END AS ROLL_SUM) FROM table_name