PHP中嵌套的While循环问题

Question

我有一个体育数据库，我有两个表，一个是事件表，一个是赔率表。我已经成功地从events表中获取了数据，我正在尝试获取从数据库中检索到的每个事件的赔率，但它需要永远加载，可能是因为我使用了多个while循环，请告诉我如何简化sql查询以减少加载时间。下面是我的代码

<?php
    include("admin/db.php");
    include("../mpdf.php");
     $mpdf = new mPDF('utf-8',    // mode - default ''
     'A4-L',    // format - A4, for example, default ''
     12,     // font size - default 0
     '',    // default font family
     2,    // margin_left
     2,    // margin right
     2,     // margin top
     2,    // margin bottom
     0,     // margin header
     0,     // margin footer
     'L');  // L - landscape, P - portrait 

    $html .="<h1 align='center'>ELSPORTBET</h1>";
    $html .="<table border=1 width='100%;' cellpadding=1>";

    $stmt = mysql_query("SELECT * FROM event ORDER BY league limit 100");

    $current_cat = null;
    while ($row =mysql_fetch_array($stmt)) {
      if ($row["league"] != $current_cat) {
        $current_cat = $row["league"];
        $html.="<tr><th colspan='3' align='center'>$current_cat</th></tr>";
      }
      $html.="<tr><td colspan='3' align='center'>$row[eventid]</td>";

     /* planning to call a while loop here , takes forever to load
     $sql4=mysql_query("select price from odds where eventid='$row[eventid]'");
      while($odds=mysql_fetch_array($sql4)){
        $html.="<tr><td colspan='3' align='center'>$odds[price]</td></tr>";  output all the odds
      } */

    }
    $html .="</table>";

    $mpdf->SetDisplayMode('fullpage');
    $stylesheet = file_get_contents('table_style.css');
    $mpdf->WriteHTML($stylesheet,1);    
    $mpdf->WriteHTML($html);
    $mpdf->Output("pdf.pdf", "I");
    exit;

?>

Answer 1

这里的问题是，您要为每个查询调用DB。为什么不这样做呢( "，“是一个内部连接)：

$stmt = mysql_query("SELECT e.league, o.price FROM event e, odds o WHERE e.eventid = o.eventid ORDER BY e.league limit 100");

$current_cat = null;
$current_id = null;
while ($row = mysql_fetch_array($stmt)) {
  if ($row["league"] != $current_cat) {
    $current_cat = $row["league"];
    $html .= "<tr><th colspan='2' align='center'>$current_cat</th></tr>";
    $html .= "<tr><td align='center'>$row[eventid]</td>";
    $html .= "<td align='center'>$row[price]</td></tr>"; 
  }
  else
  {
    if($row["eventid"] != $current_id)
    {
       $current_id = $row["eventid"];
       $html .= "</tr><tr><td align='center'>$current_id</td>";
       $html .= "<td align='center'>$row[price]</td>";
    }
    else
    {
    $html .= "<td align='center'>$row[price]</td>"; 
    }
  }
}
$html .="</tr>";

好的，这应该是可行的。