php - php + mysql_num_rows

Question

有没有更有效的方法来执行以下操作？

$total_a = mysql_query("SELECT `id` FROM `table` WHERE `this` = 'that'");
$total_b = mysql_num_rows($total_a);

if(!$total_b)
{
    echo 'no results';
}
else
{
    $a = mysql_query("SELECT `id`, `time` FROM `table` WHERE `this` = 'that' ORDER BY `time` DESC");
    while($b = mysql_fetch_assoc($a))
    {
        echo $b['id'].'-'.$b['time'].'<br />';
    }
}

除了为此使用两个查询之外，没有其他办法，是吗？

Answer 1

您现在要检索两次相同的东西，对吗？如果根据查询 1 存在某些数据，请使用查询 2 再次检索该数据并显示它。为什么不简单地使用第二个查询？

$sql = "SELECT id, time FROM table WHERE this = 'that' ORDER BY time DESC";
$res = mysql_query($sql);
if (mysql_num_rows($res)) {
  while ($b = ...) {
    ...
  }
} else {
  echo 'no results';
}

Answer 2

您应该能够像这样重用查询：

$result = mysql_query("SELECT `id`, `time` FROM `table` WHERE `this` = 'that' ORDER BY `time` DESC");
$num_rows = mysql_num_rows($result);

if(!$num_rows)
{
    echo 'no results';
}
else
{
    while($row = mysql_fetch_assoc($result))
    {
        echo $row['id'].'-'.$row['time'].'<br />';
    }
}

Answer 3

从根本上说，它们是相同的查询，不是吗？！

为什么你不能这样做：

$sql = "SELECT `id`, `time` FROM `table` WHERE `this` = 'that' ORDER BY `time` DESC";
$result = mysql_query($sql);

if(mysql_num_rows($result)){
    while($b = mysql_fetch_array($result))
    {
        echo $b['id'].'-'.$b['time'].'<br />';
    }
}
else{
  // no rows
}

Answer 4

只需使用：

$a = mysql_query("SELECT `id`, `time` FROM `table` WHERE `this` = 'that' ORDER BY `time` DESC");
while($b = mysql_fetch_assoc($a))
{
    echo $b['id'].'-'.$b['time'].'<br />';
}

为什么要数？

如果你做类似的事情，你只应该计算可能的行

if($count){
echo "starting the stuff";
$a = mysql_query("SELECT `id`, `time` FROM `table` WHERE `this` = 'that' ORDER BY `time` DESC");
while($b = mysql_fetch_assoc($a))
{
    echo $b['id'].'-'.$b['time'].'<br />';
}
echo "ending the stuff";
}