Modify a Table field by adding to it.

Question

I have Table1, where I want to modify previous_sum where previous_sum is the sum of the numbers field in Table 2 up to that specific date. Example:

Table1

Date___|___previous_sum
01/01__|___20
01/02__|___50
01/03__|___100

Table2

Date___|___numbers
01/01__|___20
01/02__|___30
01/03__|___50

So, previous_sum is 0 in the beginning but depending on what is in the numbers field up to that date, I want it to add correspondingly to previous_sum.

Answer 1

UPDATE  table1
SET     previous_sum = 
        COALESCE(
        (
        SELECT  SUM(numbers)
        FROM    table2
        WHERE   table2.date <= table1.date
        ), 0)

Answer 2

UPDATE Table1 
SET [previous_sum] = (SELECT SUM(numbers) WHERE Table2.Date <= Table1.Date)

Answer 3

I'm not quite sure what you're asking, but I think you mean something like this?

UPDATE Table1 SET Previous_Sum = Table2.numbers
FROM Table1
INNER JOIN Table2 ON Table1.Date = Table2.Date

P.S. if you need a SUM just add a group by and SUM the numbers