从 MySQL 个链接表创建 PHP 二维数组

Question

我希望有人能帮我解决这个问题。

我有2个table:

课程

+------------+--------------+
| Field      | Type         |
+------------+--------------+
| id         | int(11)      |
| name       | varchar(255) |
+------------+--------------+

文件

+------------+--------------+
| Field      | Type         |
+------------+--------------+
| id         | int(11)      |
| course_id  | int(11)      |
| name       | varchar(255) |
+------------+--------------+

我想要的代码 return 是一个二维 PHP 数组，类似于：

Array
(
    [0] => Array
        (
            [id] => 3
            [name] => Digital image processing
            [files] => Array
                (
                    [0] => Array
                        (
                            [id] => 6
                            [name] => DIP-ch02-93-1.pdf
                        )

                    [1] => Array
                        (
                            [id] => 9
                            [name] => A_brief_introduction_to_matlab.pdf
                        )

                )

        )

    [1] => Array
        (
            [id] => 1
            [name] => Artificial intelligence
            [files] => Array
                (
                    [0] => Array
                        (
                            [id] => 12
                            [name] => DIP-ch02-93-1.pdf
                        )

                    [1] => Array
                        (
                            [id] => 1
                            [name] => AI-ch03-922.pdf
                        )

                    [2] => Array
                        (
                            [id] => 2
                            [name] => AI-ch04-932.pdf
                        )

                )

        )

)

我使用 php PDO。我有以下代码：

$conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
$stmt = $conn->prepare("SELECT c.id, c.name, f.id as fid, f.name as fname FROM courses c left outer join files f on c.id=f.course_id");
$stmt->execute();

// set the resulting array to associative
$result = $stmt->setFetchMode(PDO::FETCH_ASSOC);
$courses = $stmt->fetchAll();

print_r($courses);

但它 return 我这个数组：

Array
(
    [0] => Array
        (
            [id] => 1
            [name] => Artificial intelligence
            [fid] => 1
            [fname] => AI-ch03-922.pdf
        )

    [1] => Array
        (
            [id] => 1
            [name] => Artificial intelligence
            [fid] => 2
            [fname] => AI-ch04-932.pdf
        )

    [4] => Array
        (
            [id] => 3
            [name] => Digital image processing
            [fid] => 6
            [fname] => DIP-ch02-93-1.pdf
        )

    [5] => Array
        (
            [id] => 3
            [name] => Digital image processing
            [fid] => 9
            [fname] => A_brief_introduction_to_matlab.pdf
        )

    [6] => Array
        (
            [id] => 1
            [name] => Artificial intelligence
            [fid] => 12
            [fname] => DIP-ch02-93-1.pdf
        )

)

我也有以下正确代码：

$conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
$stmt = $conn->prepare("SELECT id, name FROM courses");
$stmt->execute();

// set the resulting array to associative
$result = $stmt->setFetchMode(PDO::FETCH_ASSOC);
$courses = $stmt->fetchAll();

for($i = 0; $i < count($courses); $i++){

    $stmt = $conn->prepare("SELECT id, name FROM files where course_id=".$courses[$i]['id']);
    $stmt->execute();

    // set the resulting array to associative
    $result = $stmt->setFetchMode(PDO::FETCH_ASSOC);
    $result = $stmt->fetchAll();

    $courses[$i]['files'] = $result;
}
print_r($courses);

它 return 是正确的结果但是我想从我的代码中删除那个 for 循环。事实上，我想通过单个查询从 Mysql 中检索数据。
谁能帮帮我？

Answer 1

SELECT * 
FROM files AS f 
JOIN courses AS c ON c.id = f.course_id
WHERE course_id IN (Select id from courses)"

如果您没有课程条件，最后一行没有意义只需在子选择中添加一个 WHERE。

Answer 2

您需要重新格式化数组。 PDO 查询 return 按行显示结果。

$conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
$stmt = $conn->prepare("SELECT c.id, c.name, f.id as fid, f.name as fname FROM courses c left outer join files f on c.id=f.course_id");
$stmt->execute();

// set the resulting array to associative
$result = $stmt->setFetchMode(PDO::FETCH_ASSOC);
$courses = $stmt->fetchAll();

$formattedcourses = array();

foreach($courses as $course){
     $formattedcourses[$course['id']]['id'] = $course['id'];
     $formattedcourses[$course['id']]['name'] = $course['name'];
     $formattedcourses[$course['id']]['files'][] = array(
                  'id' =>  $course['fid'],
                  'name' => $course['fname']
     );
}

从 MySQL 个链接表创建 PHP 二维数组

Create PHP two dimensional array from MySQL linked tables

php

mysql

arrays

fetch

课程

文件