php sql help. adding rows together??

[jcrensha627]

Here is my situation:

Im trying to figure out how to add rows together to get "volume"

here an example of my table

id symbol shares volume price
13 JAME 100 100 50.00
14 JAME 50 "X" 50.00

what SQL query do i use to make the "x" in id 14 equal to the volume in 13 + shares in 14.

basically how do i have "X" replaced with 150

[jcrensha627]

i do want the number to add up so i can have an idea of the volume of the shares. this needs to be updated so the price will fluctuate with it. Also im trying to figure how to make Y fluctuate based on "X"

id symbol shares volume price
13 JAME 100 100 50.00
14 JAME 50 "X" "Y"
15
16...