php sql Get query when checkbox is checked

sorry but i'm kinda noob of this sort of things, but i just wanted to know how to get the value of a column in sql, when the checkbox is checked, then it would add up the values since they are numbers.

data

SEARCH = Dan

-----------------------
name   |   date    | Total | Checkbox
-------------------------------------
Dan    | dd/mm/yyy | 200   |  checked
Dan    | dd/mm/yyy | 400   |  checked
Dan    | dd/mm/yyy | 300   |  checked
Dan    | dd/mm/yyy | 250   |  unchecked
Dan    | dd/mm/yyy | 260   |  unchecked

TOTAL AMOUNT = 900

I'm just kinda stuck,any help would be appreciated :) again sorry for being a noob >.< here's the code