Question

我正在从代码中增加一个ID。当我从数据库中检索最大值时，它没有分配给变量。

我从数据库SQL测试查询，然后显示最大值。但是当我回声时它不会显示。

这是我的代码，

<html>
    <body>
        <form enctype="multipart/form-data" method="post" action="test_issue.php">
           <input name="submit" type="submit" id="submit" value="submit"  /> 
        </form>
    </body>
</html>

<?php
    include ("connection.php");
            if(isset($_POST['submit']))
            {               
                    // $queryselect =  "SELECT issued_id FROM pass WHERE pass_id=8";
                    $queryselect= "SELECT MAX(issued_id) FROM pass WHERE status='Issued'";
                    $last_sec_result = mysqli_query($connection,$queryselect );

                    if($last_sec_result!=0)
                    {
                        $last_sec_value = mysqli_fetch_array($last_sec_result);
                        $sec_id_no = $last_sec_value['issued_id'];
                        echo $sec_id_no;   
                    }
                    else
                    {
                        echo $last_sec_result ;
                        echo "database query failed please check data you enter.";
                    }
                    // echo $sec_id_no;
            }
?>

当我使用简单的选择查询（SELECT issued_id FROM pass WHERE pass_id=8）检索值时，它会显示该值。我坚持这一点。谁能帮我。

Answer 1

您的查询定义了列MAX(issued_id)，但没有别名，因此，在获取的记录中，它具有一些奇特的名称，例如... MAX(issued_id)。

尝试像这样更改您的查询（注意AS issued_id部分）：

SELECT MAX(issued_id) AS issued_id FROM pass WHERE status='Issued'

这将确保获取的记录具有issued_id字段，并且您的以下代码将能够提取该记录。

Answer 2

1- mysql_query（）不返回整数，因为您的条件正在等待 2-使用别名来确定返回结果集中的索引

include ("connection.php");
        if(isset($_POST['submit']))
        {               
                // $queryselect =  "SELECT issued_id as issued_id FROM pass WHERE pass_id=8";
                $queryselect= "SELECT MAX(issued_id) as issued_id FROM pass WHERE status='Issued'";
                $last_sec_result = mysqli_query($connection,$queryselect );

                if($last_sec_result !== null)
                {
                    $last_sec_value = mysqli_fetch_array($last_sec_result);
                    $sec_id_no = $last_sec_value['issued_id'];
                    echo $sec_id_no;   
                }

                else
                {
                    echo $last_sec_result ;
                    echo "database query failed please check data you enter.";
                }
                // echo $sec_id_no;
        }

Answer 3

因此，如果以前的答案没有为您提供预期的解决方案，那么没有状态设置为完全相同的内容'Issued'的行，这就是查询返回空结果数组的原因。

SELECT issued_id, status FROM pass;
# must return some rows

SELECT MAX(issued_id) AS issued_id FROM pass;
# must return some numbers

SELECT MAX(issued_id) AS issued_id FROM pass WHERE status='Issued';
# should return expected value

使用PHP从数据库中检索整数值

3 个答案: