正在尝试转换为mysqli。这几天我得到了很大的帮助，谢谢。我的下一个问题是当使用左连接时如何转换。
mysql工作代码

$q1 = 'SELECT * FROM earth LEFT JOIN cities ON (cities.countryid4city = earth.countryid) GROUP BY countryid ORDER by countryid';
$q2 = 'SELECT * FROM cities ORDER BY cityname';
$mytable1 = mysql_query($q1);
$mytable2 = mysql_query($q2);
echo mysql_error();
mysql_close();
$numrows_table1 = mysql_numrows($mytable1); 
$numrows_table2 = mysql_numrows($mytable2);
$i = 0;
while ($i < $numrows_table1){
    $countryid = mysql_result($mytable1,$i,'countryid');
    $countryname = mysql_result($mytable1,$i,'countryname');
    print "<br><br>Country is " . $countryname . ", and these cities are in it";
    $j = 0;
    while ($j < $numrows_table2){
        $countryid4city = mysql_result($mytable2,$j,'countryid4city');
        $cityname = mysql_result($mytable2,$j,'cityname');
        if ($countryid4city == $countryid){
            print "<br><br>" . $cityname;
        }
        $j++;
    }
    $i++;
}

输出如预期(请注意，此网站删除了此页中的换行符，但它们仍然存在）。

Country is USA, and these cities are in it
New York
San Francisco
Country is England, and these cities are in it
Chelsea
Clapham
London
Country is Sweden, and these cities are in it
Lidingö
Stockholm

破坏mysqli转换（遵循相同的逻辑，我想）

$q1 = 'SELECT * FROM earth LEFT JOIN cities ON (cities.countryid4city = earth.countryid) GROUP BY countryid ORDER by countryid';
$q2 = 'SELECT * FROM cities ORDER BY cityname';
$mytable1 = mysqli_query($conned, $q1);
$mytable2 = mysqli_query($conned, $q2);
mysqli_close($conned);
while($row1 = mysqli_fetch_assoc($mytable1)){
    $countryid = $row1['countryid'];
    $countryname = $row1['countryname'];
    print "<br><br>Country is " . $countryname . ", and these cities are in it";
    while($row2 = mysqli_fetch_assoc($mytable2)){
        $countryid4city = $row2['countryid4city'];
        $cityname = $row2['cityname'];
        if ($countryid4city == $countryid){
            print "<br><br>" . $cityname;
        }
    }
}

输出

Country is USA, and these cities are in it
New York
San Francisco
Country is England, and these cities are in it
Country is Sweden, and these cities are in it

它只从第二个表中选取左联接值作为第一个表的第一个值。我错过了什么？我想我可能没有一个理想的解决方案，以工作的mysql版本。
非常感谢您的帮助。谢谢。