Question

我有一个数据库存储用户根据日期添加的读数，我想根据最近添加的内容在我的HTML页面上显示读数，所以我修改了我的语句，如下所示：

public function getElecReadings(){
        try {
            $stmt = $this->dbconn->prepare("SELECT ElecReadingID, ElecUsage, DateAdded FROM elec_readings ORDER BY DESC WHERE AccountNumber = '" . $_SESSION['user_session'] . "'");
            $stmt->execute();
            return $stmt;
        } catch (Exception $e) {

        }
    }

但是，一旦我添加ORDER BY子句，我似乎在我的HTML页面上出现Warning: Invalid argument supplied for foreach()错误，我在其中回显了值，

<?php
        foreach ($elec_readings as $elec_reading): ?>
            <tbody>
                <tr>
                    <td><?php echo $elec_reading['ElecUsage']; ?></td>
                    <td><?php echo $elec_reading['DateAdded']; ?></td>
                </tr>
            ?php
        endforeach;
    ?>

知道为什么会这样吗？

Answer 1

是。你的SQL查询现在很糟糕。订单BY是在何处关闭

(SELECT ElecReadingID, ElecUsage, DateAdded FROM elec_readings WHERE [your_condition] ORDER BY [Your_Field] DESC|ASC ");

Foreach显示错误导致SQL查询失败，$elec_readings为空（或FALSE）

Answer 2

试试这样：

public function getElecReadings(){
    try {
        $stmt = $this->dbconn->prepare("SELECT ElecReadingID, ElecUsage, DateAdded FROM elec_readings WHERE AccountNumber = '" . $_SESSION['user_session'] . "' ORDER BY DESC");
        $stmt->execute();
        return $stmt;
    } catch (Exception $e) {

    }
}

<?php
    if (!empty($elec_readings)):
     foreach ($elec_readings as $elec_reading): ?>
        <tbody>
            <tr>
                <td><?php echo $elec_reading['ElecUsage']; ?></td>
                <td><?php echo $elec_reading['DateAdded']; ?></td>
            </tr>
        ?php
    endforeach;
    endif;
?>

Answer 3

您收到Warning因为您的查询无效，如果您想要使用ORDER BY和WHERE子句而不是您需要遵循此序列：

SELECT .. FROM .. WHERE .. ORDER BY ..

修改后的查询：

$stmt = $this->dbconn->prepare("
SELECT ElecReadingID, ElecUsage, DateAdded 
FROM elec_readings 
WHERE AccountNumber = '" . $_SESSION['user_session'] . "' 
ORDER BY ElecReadingID DESC");

请注意，您还需要指定更改订单所需的列，例如，我在ElecReadingID中使用ORDER BY DESC列

forEach（）无效

3 个答案: