您可能使用了错误的变量。请尝试以下操作：

public function move($data)
{
    $sku = $data['sku'];
    $store = $data['store_id'];
    $sql = "SELECT * FROM products WHERE sku = ? AND store_id = ?";
    $query = $this->db->query($sql, array($data['sku'], $data['store_id']));
    $result_array = $query->result_array();
    if($result_array) {
        $data['qty'] =  $data['qty'] + $result_array['qty'] ;  //Error here
        $insert = $this->db->query('products', $data);
        return ($insert == true) ? true : false;
    }
    else{

    }
}

$query-〉result_array（）将从数据库中返回一个满足查询条件的行数组。如果你只需要一行，你必须修改它。

public function move($data)
{
    $sku = $data['sku'];
    $store = $data['store_id'];
    $sql = "SELECT * FROM products WHERE sku = ? AND store_id = ?";
    $query = $this->db->query($sql, array($data['sku'], $data['store_id']));

if($query->num_rows() > 0){
    $row = $query->row();  // select only first row of the query result
    $data['qty'] =  $data['qty'] + $row['qty'] ;
    $insert = $this->db->query('products', $data);  // don't know what you are doing here
    return ($insert == true) ? true : false;
}else{
}
}

在mysqli_result类中

• • 表示从数据库查询中获取的结果集。*

这里主要使用两种类型
1.数组项集
1.单行
在使用mysqli_result类的格式中，有两种方法用于提取上述类别中的结果：

`1-mysqli_result::fetch_array — Fetch the next row of a result set as an associative, a numeric array, or both`

`2-mysqli_result::fetch_row — Fetch the next row of a result set as an enumerated array`

下面是PHP Codeigniter中的简单解决方案：-
我打电话给

1-示例”-

$registrations = $this->db->get_where('registration', array('school_id' => school_id()))

那就写"解决方案"

->result_array(); or ->row_array();

就像这样：-

$registrations = $this->db->get_where('registration', array('school_id' => school_id()))->result_array();

问题已解决！