mysqli查询无结果致数组偏移访问报错的问题求助

问题原因 #

当数据库查询无匹配结果时，mysqli_fetch_array()会返回null。原代码直接尝试访问$s_m_shape_2['next_review_date']，此时变量是null而非数组，因此触发Trying to access array offset on value of type null错误。

解决方案 #

核心思路是先判断查询结果是否有效（非null），再处理数组访问逻辑，同时初始化默认值避免后续报错。

修改后的关键代码如下：

$search_med_shape_2 = "select fs.shape_date,fs.shape_category,fd.next_review_date 
                     from force_shape_2 fs,force_shape_2_detail fd  
                     where fs.force_id='".$fid."'
                        and fs.force_id=fd.force_id and fd.next_review_date<>'1970-01-01 00:00:00'
                     order by shape_date desc limit 1";
$s_med_shape_2 = mysqli_query($connpis, $search_med_shape_2);
$s_m_shape_2 = mysqli_fetch_array($s_med_shape_2, MYSQLI_ASSOC);

// 处理查询结果为null的情况，初始化默认数组
if (!$s_m_shape_2) {
    $s_m_shape_2 = [
        'next_review_date' => '0',
        'shape_date' => '',
        'shape_category' => ''
    ];
} else {
    // 原有的空值处理逻辑
    if ($s_m_shape_2['next_review_date'] == "") {
        $s_m_shape_2['next_review_date'] = '0';
    }
}

$med_shape_1 = mysqli_num_rows($s_m_cat);
$med_shape_2 = mysqli_num_rows($s_med_shape_2);

// 后续逻辑可安全访问$s_m_shape_2的键
if ($med_shape_1 > '0' or $med_shape_2 > '0') {
    // 注意：需确保$s_med_cat不为null，否则会触发同类报错
    if ($s_med_cat['shape_date'] > $s_m_shape_2['next_review_date']) {
        $ind_med_shape = $s_med_cat['code']." As On ";
        $ind_med_shape_date = date("d-m-Y",strtotime($s_med_cat['shape_date']));
    }
}

额外建议 #

原代码直接将$fid拼接进SQL语句，存在SQL注入风险，建议使用mysqli预处理语句替代，示例如下：

// 使用预处理语句避免SQL注入
$search_med_shape_2 = "select fs.shape_date,fs.shape_category,fd.next_review_date 
                     from force_shape_2 fs,force_shape_2_detail fd  
                     where fs.force_id=?
                        and fs.force_id=fd.force_id and fd.next_review_date<>'1970-01-01 00:00:00'
                     order by shape_date desc limit 1";
$stmt = mysqli_prepare($connpis, $search_med_shape_2);
mysqli_stmt_bind_param($stmt, "s", $fid);
mysqli_stmt_execute($stmt);
$s_med_shape_2 = mysqli_stmt_get_result($stmt);
$s_m_shape_2 = mysqli_fetch_array($s_med_shape_2, MYSQLI_ASSOC);

内容的提问来源于stack exchange，提问作者suman singh