PHP mysql需要协助处理带有和没有设置值的var

Question

$read2 = "SELECT * FROM `elmtree_transactions` WHERE sellerid ='$sellerid'";
if ($result2 = $conn->query($read2)) {
    while ($row2 = $result2->fetch_assoc()) {
        $rating = $row2['rating'];
    }
}
echo "                  
    <div class='col-sm-3 pt-3'>
    <div class='card'>
    <div class='card-header'>
        <strong>$user</strong><br>
        Seller Rating : $rating / 5 <img src='/elmtree/images/star.png' class=' img-rating' />
        </div>
    ";

设置卖家评分。如果卖家在MySQL表中有评级，则会在页面上显示。如果他们不这样做会引发错误导致$rating var未定义，这会导致网页看起来坏了。想要管理这个并且在MySQL表中没有评级时显示0/5或“卖家没有评级”的打包

Answer 1

你的mysql查询只会在mysql返回的值时循环显示

在OP中，没有真正准确的错误定义。但我现在假设你遇到一个关于尚未初始化的变量的警告错误。

所以，通过良好的实践，我会在那个循环之前初始化变量$rating

$rating = null;
$read2 = "SELECT * FROM `elmtree_transactions` WHERE sellerid ='$sellerid'";
if ($result2 = $conn->query($read2)) {
    while ($row2 = $result2->fetch_assoc()) {
        $rating = $row2['rating'];
    }
}
echo "                  
    <div class='col-sm-3 pt-3'>
    <div class='card'>
    <div class='card-header'>
        <strong>$user</strong><br>
        ".(is_numeric($rating)?"Seller Rating : $rating / 5 <img src='/elmtree/images/star.png' class=' img-rating' />":'No rating available yet')."
        </div>
    ";