Author: Tomas Rutkauskas 

I am upgrading an application and need to add fields to a Paradox TTable database. 
The application should inspect the existing database file structure and upgrade the 
customers existing database if necessary.

Answer:

First, open the files using a TTables exclusively, and check for fields. I was 
adding fields so I used the following code:

1   with tblEmployer do
2   begin
3     open;
4     lFoundAddCalcMethod := FindField('RetireCalcMethod') <> nil;
5     lFoundRetireFundMethod := FindField('RetireFundMethod') <> nil;
6     close;
7   end;


If I was altering a field (for example, say I wanted to make a field change from 
Integer to String), you could assing the result of FindField to a TField variable 
and check it. Then I alter the table as needed:

8   if not lFoundAddCalcMethod then
9     QryAddRetireCalcMethod.ExecSQL;


and the SQL part of the TQuery:

alter table "MAXXEMPL.DB"
add RetireCalcMethod character(2),
add RetireFundDollar Float,
add RetireFundPercent Float,
add LocalTaxMthd character(2);