CREATE TABLE table_example
(
    id INTEGER NOT NULL PRIMARY KEY
    data INTEGER
);

CREATE GENERATOR generator_name;
SET TERM ^ ;
CREATE TRIGGER trigger_name FOR table_example ACTIVE
BEFORE INSERT POSITION 1
AS 
BEGIN 
    if (new.id is null ) then
    new.id = gen_id (generator_name, 1);
END^
SET TERM ; ^

procedure TForm1.Button2Click(Sender: TObject);
begin
 fdtable2.insert;
    fdtable2.FieldByName('data').Value:= 'test';
    fdtable2.post;
end;