php + mysql_num_rows

Question

是否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 />';
    }
}

除了使用两个查询之外别无他法，是吗？

Answer 1

你现在两次检索同一件事，对吧？如果根据查询1存在某些数据，则使用查询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

您应该能够重复使用这样的查询：

$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，他们是相同的查询，不是吗？！

你为什么不能这样做：

$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 />';
}

为何算数？

如果您执行类似

的操作，则只应计算可能的行数

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";
}