Get value from one table and subtract it from a similar value in a different table?

[imhiya]

Calculations and updating tables
Ok, i have two tables,

one called Feed Schedule, in it is has Type of food and Quantity Fields

So it looks like this

Type of Food Quantity
Cat Null
Dog 2


Then i have another table called Stock, it has the same layout but has the current stock for each of the above and looks like this

Type of Food Quantity
Cat 2000
Dog 2000

What i am wanting to do is update cat and dog quantitys in the stock table with the stock removed, so it would result with

Type of Food Quantity
Cat 2000
Dog 1998

I want it to do this when i either run a macro or a query using sql. But i am sure how to do this.

Please help with the programming, thank you in advance

 

[imhiya]

any advice would be appreciated mainly i want to know if its possible