从特定行中减去两列

Question

I have a table similar to the one below:

           
1         3            1             2
2         1            3            -2
3         23           7             16
4         5            1             4
5         7            5             2
6         2            2             0
7         9            1             8

How do i Come up with the Vote_Total?

Answer 1

尝试这个：

update mytable set vote_total = vote_up - vote_down

Answer 2

If you already have the column,and want to update @ssamuel's answer will guide you. If you do not have the Vote_Down column, and wanted to select it as a column in query. This would be the select query :

SELECT ID  ,  Vote_Up ,  Vote_Down , ( Vote_Up - Vote_Down)
as Vote_Total from myVotesTable

Assumed : Vote_Up and Vote_Down are integer or varchar fields with numeric values.