Question

我有一个带有邻接列表方法的数据库来处理产品的分类，其中可以在许多类别下找到一种产品。查看以下数据库布局：

cats
id    parent    title           desc
1     0         top             top level
2     1         Electronics
3     2         Gaming
4     2         Computers
5     4         Tablets
6     1         Food
7     3         Xbox

products
id        title         qty
1         ToshibaTV     5
2         I-PAD2        9
3         Laser Pen     24
4         Asus Notebook 5


cats_products
id   product_id   cat_id 
1    2            3
2    2            5
3    1            2
4    3            2
5    4            4

在上面的示例中，我需要一个SQL查询，它能够检索在电子类别中找到的所有产品及其任何级别的任何子类别（例如Xbox不是直接子级的）电子产品）不重复在I-PAD2等多个类别中发现的产品。

我可以在PHP的应用程序的帮助下做到这一点，但我想知道是否可以在MySQL中使用纯SQL来实现它？

Answer 1

使用邻接列表模型，您要做的事情相当困难。正如@Mike建议的那样，使用嵌套集模型会使这更容易。或者通过您的PHP代码执行它甚至会更容易。

但是，假设您知道可能有多少个父子级别（或者您可以假设不会超过X个），您可以尝试这样的事情。如果MySQL支持CTE，这将更容易阅读，但不幸的是，它没有。在这个例子中，我已经深入了4级 - 你可以深入了解。

SELECT p.Id, p.Title, p.Qty
FROM Products p
   JOIN Cats_Products cp on p.id = cp.product_id
WHERE cp.cat_id IN (
   SELECT c.id
   FROM Cats c
   WHERE c.title = 'Electronics'
   UNION ALL
   SELECT c2.id
   FROM Cats c
      LEFT JOIN Cats c2 ON c.id = c2.parent
   WHERE c.title = 'Electronics'
   UNION ALL
   SELECT c3.id
   FROM Cats c
      LEFT JOIN Cats c2 ON c.id = c2.parent
      LEFT JOIN Cats c3 ON c2.id = c3.parent
   WHERE c.title = 'Electronics'
   UNION ALL
   SELECT c4.id
   FROM Cats c
      LEFT JOIN Cats c2 ON c.id = c2.parent
      LEFT JOIN Cats c3 ON c2.id = c3.parent
      LEFT JOIN Cats c4 ON c3.id = c4.parent
   WHERE c.title = 'Electronics'
)
GROUP BY p.Id, p.Title, p.Qty

这是SQL Fiddle。

祝你好运。

Answer 2

这是你问的第一部分。你能否更详细地解释孩子的部分？我想这与猫的父母有关。

试试这个：

SELECT distinct(p.title) 
FROM cats AS c
JOIN cats_products AS cp
ON cp.cat_id = c.id AND c.title = "Electronics"
JOIN products AS p
ON p.id = cp.product_id;

示例数据：

CREATE TABLE cats
    (`id` int, `parent` int, `title` varchar(11), `desc` varchar(9))
;

INSERT INTO cats
    (`id`, `parent`, `title`, `desc`)
VALUES
    (1, 0, 'top', 'top level'),
    (2, 1, 'Electronics', ''),
    (3, 2, 'Gaming', ''),
    (4, 2, 'Computers', ''),
    (5, 4, 'Tablets', ''),
    (6, 1, 'Food', ''),
    (7, 3, 'Xbox', '')
;



CREATE TABLE products
    (`id` int, `title` varchar(13), `qty` int)
;

INSERT INTO products
    (`id`, `title`, `qty`)
VALUES
    (1, 'ToshibaTV', 5),
    (2, 'I-PAD2', 9),
    (3, 'Laser Pen', 24),
    (4, 'Asus Notebook', 5)
;



CREATE TABLE cats_products
    (`id` int, `product_id` int, `cat_id` int)
;

INSERT INTO cats_products
    (`id`, `product_id`, `cat_id`)
VALUES
    (1, 2, 3),
    (2, 2, 5),
    (3, 1, 2),
    (4, 3, 2),
    (5, 4, 4)
;

SQL FIDDLE DEMO

编辑第二部分：

SELECT distinct(v.title) FROM products AS v
JOIN (
  SELECT Y.product_id FROM cats_products AS Y
    JOIN(
      SELECT distinct(z.id) FROM cats AS Z
        JOIN
          (SELECT c.parent
           FROM cats AS c
           JOIN cats_products AS cp
           ON cp.cat_id = c.id 
           AND c.title = "Electronics") AS X
         ON x.parent = z.parent) AS W
    ON W.id = Y.cat_id) AS u
ON u.product_id = v.id
;

示例数据

CREATE TABLE cats
    (`id` int, `parent` int, `title` varchar(11), `desc` varchar(9))
;

INSERT INTO cats
    (`id`, `parent`, `title`, `desc`)
VALUES
    (1, 0, 'top', 'top level'),
    (2, 1, 'Electronics', ''),
    (3, 2, 'Gaming', ''),
    (4, 2, 'Computers', ''),
    (5, 4, 'Tablets', ''),
    (6, 1, 'Food', ''),
    (7, 3, 'Xbox', '')
;



CREATE TABLE products
    (`id` int, `title` varchar(13), `qty` int)
;

INSERT INTO products
    (`id`, `title`, `qty`)
VALUES
    (1, 'ToshibaTV', 5),
    (2, 'I-PAD2', 9),
    (3, 'Laser Pen', 24),
    (4, 'Asus Notebook', 5),
    (5, 'French Fries', 50)
;



CREATE TABLE cats_products
    (`id` int, `product_id` int, `cat_id` int)
;

INSERT INTO cats_products
    (`id`, `product_id`, `cat_id`)
VALUES
    (1, 2, 3),
    (2, 2, 5),
    (3, 1, 2),
    (4, 3, 2),
    (5, 4, 4),
    (5, 5, 6)

;

这是我对您的问题的解释：每个类别都有父级，您希望选择具有相同父级的所有其他类别。更具体的所有产品具有相同的父类别。 SQL FIDDLE DEMO

用于检索邻接列表模型中某些类别下的所有产品的SQL查询

2 个答案: