Column Equaling Sum of Two Other Columns

[BK201]

I only have a pretty basic understanding of SQL just enough thats gotten me by whenever I needed to use a database for whatever I was writing. I can't seem to find an answer to my specific question via google. I want the value of say column 3 to equal the difference of column 2 - column 1 for every row in the table. I don't have to update a existing database, I'm working on a text-based rpg and working on creating the database.

[requinix]

You don't need that third column. You already know what its values are so there's no point in storing it. It would just mean more data you have to insert and update.

 

SELECT column1, column2, column2 - column1 AS column3, ...

Or just do the math in your code.

$column3 = $row["column2"] - $row["column1"];