Pues a mi me funciono esto:
Código Delphi
[-]
procedure TForm1.BitBtn1Click(Sender: TObject);
begin
QUERY1.SQL.TEXT:='BACKUP LOG MIBASE WITH TRUNCATE_ONLY';
QUERY1.ExecSQL;
QUERY1.SQL.TEXT:='DBCC SHRINKDATABASE ( MIBASE , TRUNCATEONLY )';
QUERY1.ExecSQL;
end;
