PHP + SQL，正确的带有父子类别和项目的tre [关闭]

Question

我正在尝试显示正确的数据树，但我是股票，所以我希望有人能指出我正确的方向。

我已经尝试过使用 PHP 代码和纯 SQL 代码，让我先展示一下到目前为止我尝试过的内容。

public function supported($ids) {
        
        $arr = json_decode($ids, true);
        
        $STH = $this->dbh->query("SELECT cid,device FROM supported_devices WHERE id IN (".implode(',',$arr).")");
        
        $a = $STH->fetchAll();
        
        if(count($a)) {
            
            foreach($a as $b) {
                $newArr[] = $b['cid'];
            }
            
            $STH = $this->dbh->query("SELECT cid,cat_name FROM supported_devices_cats WHERE id IN (".implode(',',$newArr).")");

            $c = $STH->fetchAll();
            
            foreach($c as $d) {
                $newArr2[] = $d['cid'];
            }
            
            $STH = $this->dbh->query("SELECT cat_name FROM supported_devices_cats WHERE id IN (".implode(',',$newArr2).")");

            $e = $STH->fetchAll();
            
            foreach($e as $parent) {
                $return[] = $parent['cat_name'];
                foreach($c as $child) {
                    $return[] = $child['cat_name'];
                    foreach($a as $device) {
                        $return[] = $device['device'];
                    }
                }
            }
            
            return $return;
            
        } else {
            return array();
        }
    }

SELECT DISTINCT c.*
FROM supported_devices_cats c
    LEFT JOIN supported_devices_cats pc
    ON c.id = pc.cid
WHERE
    c.cid IS NOT NULL 
    OR (c.cid IS NULL
       AND pc.cid IS NULL)

我正在尝试首先显示父类别，然后是所有子类别，然后是每个子类别下的正确设备。我不知道我还能如何解释它，我添加了一幅画，也许这更好地解释了我正在尝试做的事情。

更新，我需要将我的 MySQL 服务器升级到更高版本。

Answer 1

我不太确定为什么您需要在表supported_devices 中添加一个“cid”列。外键只需 id 即可。

话虽如此，这是我用作数据库架构和测试内容的内容：

CREATE DATABASE cats_devs;

USE cats_devs

CREATE TABLE supported_devices_cats(
    id INT PRIMARY KEY,
    cid INT NULL DEFAULT NULL,
    FOREIGN KEY(cid) REFERENCES supported_devices_cats(id),
    cat_name VARCHAR(64) NOT NULL,
    dt DATETIME NOT NULL DEFAULT NOW()
);

CREATE TABLE supported_devices(
    id INT,
    FOREIGN KEY(id) REFERENCES supported_devices_cats(id),
    device VARCHAR(128) NOT NULL,
    dt DATETIME NOT NULL DEFAULT NOW()
);

INSERT INTO supported_devices_cats(id, cid, cat_name) VALUES
(1, NULL, "Disk Drives"), (2, NULL, "Monitors"),
(3, 1, "SSD"), (4, 1, "HDD"), 
(5, 2, "TN"), (6, 2, "IPS");

INSERT INTO supported_devices(id, device) VALUES
(4, "Seagate 2TB"), (4, "WD 2TB"),
(3, "Corsair 256GB"), (3, "WD 256GB"),
(5, "ASUS 27in"), (5, "ASUS 21in"),
(6, "Viewsonic 27in"), (6, "LG 24in");

接下来我要做的是 CTE 递归查询（在较新的 MySQL/MariaDB 服务器中可用 - 对于旧版本，需要与 SELF JOIN 等效）：

WITH RECURSIVE hier_query(id, cat_id, cat_name, dev_name, dt) AS(
    SELECT id, cid, cat_name, CAST(NULL AS VARCHAR(128)), dt
    FROM supported_devices_cats
    WHERE cid IS NULL
    UNION ALL
    SELECT supported_devices_cats.id, supported_devices_cats.cid, 
           supported_devices_cats.cat_name, supported_devices.device, supported_devices_cats.dt
    FROM supported_devices_cats
    JOIN hier_query
         ON hier_query.id = supported_devices_cats.cid
    LEFT JOIN supported_devices ON supported_devices.id = supported_devices_cats.id
)
SELECT id, cat_id, cat_name, dev_name, dt
FROM hier_query;

这将产生以下结果，其中包含所有必需的信息：

+------+--------+-------------+----------------+---------------------+
| id   | cat_id | cat_name    | dev_name       | dt                  |
+------+--------+-------------+----------------+---------------------+
|    1 |   NULL | Disk Drives | NULL           | 2020-06-25 07:52:39 |
|    2 |   NULL | Monitors    | NULL           | 2020-06-25 07:52:39 |
|    3 |      1 | SSD         | Corsair 256GB  | 2020-06-25 07:52:39 |
|    3 |      1 | SSD         | WD 256GB       | 2020-06-25 07:52:39 |
|    4 |      1 | HDD         | Seagate 2TB    | 2020-06-25 07:52:39 |
|    4 |      1 | HDD         | WD 2TB         | 2020-06-25 07:52:39 |
|    5 |      2 | TN          | ASUS 27in      | 2020-06-25 07:52:39 |
|    5 |      2 | TN          | ASUS 21in      | 2020-06-25 07:52:39 |
|    6 |      2 | IPS         | Viewsonic 27in | 2020-06-25 07:52:39 |
|    6 |      2 | IPS         | LG 24in        | 2020-06-25 07:52:39 |
+------+--------+-------------+----------------+---------------------+

现在在这个结果表中，当 dev_name 为 NULL 时，它是一个父类别。您可以通过这种方式从中获取所有父类别。然后对于每个父类别，当您将 id 与 cat_id 进行比较时，您可以找到子类别。终于可以轻松搞定所有设备了。

老实说，我试图使其成为“全 SQL”解决方案，但我很难按照您想要的方式对该表进行排序。我敢打赌，其他人会做得更好。

附：这是排序问题的快速肮脏技巧。我用“->”分隔符连接子名称之前的主要类别。这样您以后可以轻松拆分它们。

WITH RECURSIVE hier_query(id, cat_id, cat_name, dev_name, dt) AS(
    SELECT id, cid, cat_name, CAST(NULL AS VARCHAR(128)), dt
    FROM supported_devices_cats
    WHERE cid IS NULL
    UNION ALL
    SELECT supported_devices_cats.id, supported_devices_cats.cid, 
           CONCAT(hier_query.cat_name, "->", supported_devices_cats.cat_name), 
           supported_devices.device, supported_devices_cats.dt
    FROM supported_devices_cats
    JOIN hier_query
         ON hier_query.id = supported_devices_cats.cid
    LEFT JOIN supported_devices ON supported_devices.id = supported_devices_cats.id
)
SELECT id, cat_id, cat_name, dev_name, dt
FROM hier_query
ORDER BY cat_name;

产生：

+------+--------+------------------+----------------+---------------------+
| id   | cat_id | cat_name         | dev_name       | dt                  |
+------+--------+------------------+----------------+---------------------+
|    1 |   NULL | Disk Drives      | NULL           | 2020-06-25 07:52:39 |
|    4 |      1 | Disk Drives->HDD | Seagate 2TB    | 2020-06-25 07:52:39 |
|    4 |      1 | Disk Drives->HDD | WD 2TB         | 2020-06-25 07:52:39 |
|    3 |      1 | Disk Drives->SSD | Corsair 256GB  | 2020-06-25 07:52:39 |
|    3 |      1 | Disk Drives->SSD | WD 256GB       | 2020-06-25 07:52:39 |
|    2 |   NULL | Monitors         | NULL           | 2020-06-25 07:52:39 |
|    6 |      2 | Monitors->IPS    | Viewsonic 27in | 2020-06-25 07:52:39 |
|    6 |      2 | Monitors->IPS    | LG 24in        | 2020-06-25 07:52:39 |
|    5 |      2 | Monitors->TN     | ASUS 27in      | 2020-06-25 07:52:39 |
|    5 |      2 | Monitors->TN     | ASUS 21in      | 2020-06-25 07:52:39 |
+------+--------+------------------+----------------+---------------------+

您甚至可以添加“WHERE cat_id IS NOT NULL”条件来删除两个无用的行。所有其他行都包含您需要的内容。