Using SQL Create Table with Dbase 7 files

I can Create Table in Access with through the (Delphi 4
C/S)DBexplorer/SQLexplorer just fine.
But the primary key does not want to work with DBase 7 (any suggestions)

create table tablename
(a char (1),b char(2),
primary key (a,b))

Should I use a constraint? Any suggestions with a sample piece of code would
be helpful