我要呈现给你的代码不起作用。未显示 IF 条件的结果。但对于其他是。当我单独调用 $service_id 时，它会给我搜索的 ID，但在 WHERE 关闭中使用时：service_id = '$service_id'，什么都不显示。
<form method="GET" name="pesquisa" id="inserrifo" action="/services.php">
<input class="procurasalgo" id='pesqSign' name="keyword" value="<?php echo $keyword;?>" placeholder="Inserir palavra"/><label for="pesqSign" id="pesqSigne"><img class="lupapesquisa" src="/img/search-26.png" /></label>
<select name="services">
<option disabled selected value=''>Serviços</option>
<?php
$res = $DAL->mysqlQuery("SELECT * FROM services");
while($row = mysql_fetch_assoc($res)){
echo "<option value='".$row['serv_id']."'>".$row['serv_name']."</option>";
}
?>
</select>
<select name='distritos'>
<option disabled selected value=''>Portugal</option>
<?php
$res = $DAL->mysqlQuery("SELECT * FROM distritos");
while($row = mysql_fetch_assoc($res)){
echo "<option value='".$row['d_id']."'>".$row['d_nome']."</option>";
}
?>
</select>
<button>Procurar</button>
</form>
" 占位符="Inserir palavra"/> 塞尔维索斯 mysqlQuery（"SELECT * FROM services"）; while（$row = mysql_fetch_assoc（$res））{ 回显 ".$row['serv_name']."; } ?> 葡萄牙 mysqlQuery（"SELECT * FROM distritos"）; while（$row = mysql_fetch_assoc（$res））{ 回显 ".$row['d_nome']."; } ?> 采购
<?php
$service_id = $_GET['services'];
$district_id = $_GET['distritos'];
$keywords = $_GET['keyword'];
if ($service_id != '' || $district_id != '' || $keywords != '') {
$result = $DAL->mysqlQuery("SELECT * FROM users, services, distritos, users_services WHERE u_id = user_id && service_id = '$service_id' && distrito_id = '$district_id' ");
$row = mysql_fetch_assoc($result);
while($row = mysql_fetch_assoc($result)) {
$img_user = $row['u_foto'];
echo "<div class='Services'><img src='http://mufip.pt/images/userimages/avatars/".$img_user."' /><br /><h5>".$row['u_name']."<h5><h6>".substr($row['u_descricao'],0, 140)."</h6></div>";
} //while
} //if
else {
$result = $DAL->mysqlQuery("SELECT * FROM users, services, distritos, users_services WHERE u_id = user_id && service_id = serv_id && distrito_id = d_id ORDER BY RAND()");
$num = mysql_numrows($result);
echo $num." resultados<br />";
while($row = mysql_fetch_assoc($result)) {
$img_user = $row['u_foto'];
echo "<div class='Services'><img src='http://mufip.pt/images/userimages/avatars/".$img_user."' /><br /><h5>".$row['u_name']."<h5><h6>".substr($row['u_descricao'],0, 140)."</h6></div>";
} //while
} //else
?>
if ($service_id != '' || $district_id != '' || $keywords != '') {
行正在检查是否存在三个之间的任何字段。换句话说，当 $service_id 或 $district_id 或 $keywords 不为空时，此逻辑检查将给出 TRUE。假设，用户只输入了"关键字"的值，在此页面中，您将获得仅$keywords的值，$service_id 和 $district_id 将为空。
由于其中一个（此处$keywords）不为空，IF 语句将返回 true，程序控制将在其中移动。
但是，在SQL查询中，您使用的是AND条件，并且需要在service_id和distrito_id列中使用有效或非空值。由于其中一个可能保持为空，因此此查询不会产生任何结果。
若要调试这种情况，请仅从其中一个下拉列表中选择值，并使用 echo 语句在 IF 块内打印查询。
我得到了朋友的帮助:)
public function returnSelectService($nomeSelect,$idSelect,$nomeCampo,$stringSQL,$selected = null)
{
$list = "<select class='"selectServicesList'" id='"$idSelect'" name='"$nomeSelect'">";
$list .="<option value='"'">Serviços</option>";
$res = $this->mysqlQuery($stringSQL);
$select = "";
while ($linha = mysql_fetch_object($res))
{
if($selected != null && $selected == $linha->serv_id)
$select = 'selected="selected"';
$list .="<option $select value='"$linha->serv_id'">".$linha->$nomeCampo."</option>";
$select = "";
}
$list .= "</select>";
return $list;
}
public function returnSelectDistrict($nomeSelect,$idSelect,$nomeCampo,$stringSQL,$selected = null)
{
$list = "<select class='"selectServicesList'" id='"$idSelect'" name='"$nomeSelect'">";
$list .="<option value='"'">Portugal</option>";
$res = $this->mysqlQuery($stringSQL);
$select = "";
while ($linha = mysql_fetch_object($res))
{
if($selected != null && $selected == $linha->d_id)
$select = 'selected="selected"';
$list .="<option $select value='"$linha->d_nome'">".$linha->$nomeCampo."</option>";
$select = "";
}
$list .= "</select>";
return $list;
}
<form method="GET" name="pesquisa" id="inserrifo" action="/services.php">
<br />
<?php
echo $DAL->returnSelectService('services','services','serv_name',"SELECT * FROM services ",$service_id);
?>
<?php
echo $DAL->returnSelectDistrict('distritos','distritos','d_nome',"SELECT * FROM distritos ",$d_id);
?>
<button class="btn btn-default">Procurar</button>
</form>
<?php
$stringSQL ="SELECT * FROM users, services, distritos, users_services WHERE u_id = user_id AND service_id = serv_id AND distrito_id = d_id ";
if($service_id != "")
$stringSQL .=" AND serv_id = '{$service_id}' ";
if($district_id != "")
$stringSQL .="AND d_id = '{$district_id}' ";
$stringSQL .="ORDER BY RAND()";
$result = $DAL->mysqlQuery($stringSQL);
$num = mysql_numrows($result);
echo $num." resultados<br />";
while($row = mysql_fetch_assoc($result)) {
$img_user = $row['u_foto'];
echo "<div class='services'>
<div class='servicesBox'>
<img src='http://mufip.pt/images/userimages/avatars/".$img_user."' />
<h4>".$row['u_name']."</h4><br />
<h5>".$row['serv_name'].", ".$row['d_nome']."</h5><br />
<p>".substr($row['u_descricao'],0, 200)." ...</p>
</div>
</div>
<div style='clear: both; background-color: white; height: 15px'>
</div>";
}
?>