if (qry_main.DatabaseName<>'')
and (datasource_main.DataSet=qry_main)
and (dbgrid_main.DataSource.Name='DataSource_main')
and (qry_main.SQL.text<>'') then
try
qry_main.Open;
except
showmessage('ERROR:'+#13+'failed to connect the database server !!!');
raise;
end;