php - MYSQL 错误 - 使用 PHP For LOOP

Question

我知道当涉及语法错误时不应该提出问题，但是，我完全不知道为什么会抛出以下错误:

PHP 和 MYSQL 代码

//Possible size array to loop through when checking quantity
    $con_size = array (26,28,30,32,33,34,35,355,36,365,37,375,38,385,39,395,
                       40,405,41,415,42,425,43,435,44,445,45,455,46,465,47,475,48,485);
    $arrayLength=count($con_size);

        for($x=0;$x<$arrayLength;$x++)
        {

    // check if size is available
    if($line['quantity_c_size_'.$con_size[$x].'_con_b'] > 0 )
    {

        $quantity = $line['quantity_c_size_'.$con_size[$x].'_con_b'];
        $current = $line['quantity_c_size_'.$con_size[$x]];
        $id = $line ['product_id'];


        $data = "UPDATE product_test
        SET quantity_c_size_$con_size[$x] = $quantity + $current,
        quantity_c_size_$con_size[$x]_con_b = 0
        WHERE product_id = $id";

        $result2 = mysql_query($data);

        if ($result2)
        {
            echo 'Stock Updated <br />';
        }
        else
        {
            echo mysql_error();
            echo '<br />';
        }
    }
}

MYSQL 错误

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ' quantity_c_size_40_con_b = 0 WHERE product_id = 12897' at line 2

我已使用上面相同的 UPDATE 语法在 PHPMyAdmin 中尝试了 MYSQL 查询，并且查询成功完成。然而，当它在 PHP FOR 循环中运行时，它会抛出上述错误。

我可能错过了一些完全明显的东西，但现在我被难住了。

有什么建议吗？谢谢

Answer 1

按照Andrew的建议，我回显了UPDATE查询，发现$current变量为NULL，因此语句中的加法计算无法完成。

我将代码修改如下:

//Possible size array to loop through when checking quantity
    $con_size = array (26,28,30,32,33,34,35,355,36,365,37,375,38,385,39,395,
                       40,405,41,415,42,425,43,435,44,445,45,455,46,465,47,475,48,485);
    $arrayLength=count($con_size);

        for($x=0;$x<$arrayLength;$x++)
        {

    // check if size is available
    if($line['quantity_c_size_'.$con_size[$x].'_con_b'] > 0 )
    {

        $quantity = $line['quantity_c_size_'.$con_size[$x].'_con_b'];

        if ($line['quantity_c_size_'.$con_size[$x]] == NULL)
        {
            $current = '0';
        }
        else
        {
            $current = $line['quantity_c_size_'.$con_size[$x]];

        }

        $id = $line ['product_id'];


        $data = "UPDATE product_test
        SET quantity_c_size_{$con_size[$x]} = $quantity + $current,
        quantity_c_size_{$con_size[$x]}_con_b = 0
        WHERE product_id = $id";

        ...