how do i put an expression in a table

[Guest]

i need to subtract column b from column a in a table. column c is where i
need the answer. i have read the "help" but did not see anything that shows
how to add an expression to find the difference. i know it must be simple,
but how do i do this?

 

[Joan Wild]

You don't do it in a table. Create a query based on the table, and put your
expression in a column in the query grid:
Expr1: [Column B] - [Column A]

 

[Douglas J. Steele]

You don't want to do that. Calculations should seldom (if ever) be stored in
tables.

As fellow Access MVP John Vinson likes to say "Storing calculated data
generally accomplishes only three things: it wastes disk space, it wastes
time (a disk fetch is much slower than almost any reasonable calculation),
and it risks data validity, since once it's stored in a table either the
Total or one of the fields that goes into the total may be changed, making
the value WRONG."

Create a query that has all of the fields in the table in it. Add a computed
column [column a] - [column b]. Use the query wherever you would have used
the table.