为什么在我的嵌套集合层次结构中我的 HAVING 子句没有正确比较 int 值？

Question

我正在使用嵌套集模型在 postgres 中为类别层次结构建模，如说明 here。我正在使用查询来查找节点的直接下属，该节点在以下文章的摘录中进行了解释：

Imagine you are showing a category of electronics products on a retailer web site. When a user clicks on a category, you would want to show the products of that category, as well as list its immediate sub-categories, but not the entire tree of categories beneath it. For this, we need to show the node and its immediate sub-nodes, but no further down the tree. For example, when showing the PORTABLE ELECTRONICS category, we will want to show MP3 PLAYERS, CD PLAYERS, and 2 WAY RADIOS, but not FLASH.

This can be easily accomplished by adding a HAVING clause to our previous query:
SELECT node.name, (COUNT(parent.name) - (sub_tree.depth + 1)) AS depth
FROM nested_category AS node,
        nested_category AS parent,
        nested_category AS sub_parent,
        (
                SELECT node.name, (COUNT(parent.name) - 1) AS depth
                FROM nested_category AS node,
                        nested_category AS parent
                WHERE node.lft BETWEEN parent.lft AND parent.rgt
                        AND node.name = 'PORTABLE ELECTRONICS'
                GROUP BY node.name
                ORDER BY node.lft
        )AS sub_tree WHERE node.lft BETWEEN parent.lft AND parent.rgt
        AND node.lft BETWEEN sub_parent.lft AND sub_parent.rgt
        AND sub_parent.name = sub_tree.name GROUP BY node.name HAVING depth <= 1 ORDER BY node.lft;

我的架构在以下方面与文章架构略有不同：

我正在使用 postgres。文章正在使用 MySql.
我的类别定义位于单独的 table
我的层次结构 table 称为 category_tree。文章称他们为nested_category

这是我的类别table定义：

(
    category_id uuid NOT NULL,
    name text COLLATE pg_catalog."default" NOT NULL,
    description text COLLATE pg_catalog."default",
    created_at timestamp with time zone NOT NULL,
    updated_at timestamp with time zone NOT NULL,
    updated_by text COLLATE pg_catalog."default" NOT NULL,
    image_url text COLLATE pg_catalog."default",
    is_main boolean NOT NULL DEFAULT false,
    CONSTRAINT category_category_id_pk PRIMARY KEY (category_id),
    CONSTRAINT category_category_name_key UNIQUE (name)
)

这是我的类别树 table 定义：

(
    category_tree_id uuid NOT NULL,
    category_id uuid NOT NULL,
    lft integer NOT NULL,
    rgt integer NOT NULL,
    created_at timestamp with time zone NOT NULL,
    updated_at timestamp with time zone NOT NULL,
    updated_by text COLLATE pg_catalog."default" NOT NULL,
    CONSTRAINT category_tree_pkey PRIMARY KEY (category_tree_id)
)

我已将文章中的查询翻译为适合我的数据库中的架构如下：

SELECT node.category_tree_id,
       node.category_id,
       cat.name,
       node.lft,
       node.rgt,
       ( Count(parent.category_tree_id) - ( sub_tree.depth + 1 ) ) AS depth,
       node.created_at,
       node.updated_at,
       node.updated_by
FROM   category_tree AS node
       JOIN category cat
         ON cat.category_id = node.category_id,
       category_tree AS parent,
       category_tree AS sub_parent,
       (SELECT node.category_tree_id,
               ( Count(parent.category_tree_id) - 1 ) AS depth
        FROM   category_tree AS node,
               category_tree AS parent
        WHERE  node.lft BETWEEN parent.lft AND parent.rgt
               AND node.category_tree_id = 'f47f6269-9605-459e-a319-2b0177f9f4d0' //lookup by category tree id
        GROUP  BY node.category_tree_id
        ORDER  BY node.lft) AS sub_tree
WHERE  ( node.lft BETWEEN parent.lft AND parent.rgt )
       AND ( node.lft BETWEEN sub_parent.lft AND sub_parent.rgt )
       AND ( sub_parent.category_tree_id = sub_tree.category_tree_id )
GROUP  BY node.category_tree_id,
          depth,
          cat.name
HAVING depth <= 1
ORDER  BY node.lft

此查询没有产生任何结果，问题似乎来自 HAVING depth ... 子句。我的 category_tree table 中有两行 depth 的值分别是 0 和 1，如下所示：

"f47f6269-9605-459e-a319-2b0177f9f4d0", "d06a143b-523e-4136-8a17-1049abbf76f4", "Parent", 7, 10, 0
"14b939e9-6784-4905-ba24-f67768c57085", "21191930-a5b9-4868-883f-3798f29d70a3", "Child", 8, 9,  1

奇怪的是，如果我更改子句 HAVING depth > 1 我实际上得到了我期望的两个结果，这显然是错误的。

我的问题是什么？

Answer 1

我在 MySQL 上测试了您的查询，我发现您在外部查询中定义的 depth 别名与子查询的列 subtree.depth.

不明确

如果我将外部查询的别名重命名为不同的名称，例如depth2，并在 HAVING depth2 <= 1 中引用它，如您所料，我得到了“parent”和“child”的两行。

Answer 2

回答我自己的问题。

您不能在定义它的同一级别上使用列别名，并且只允许在使用聚合的查询中使用。如果要避免重复表达式，请使用派生的 table。 -source

完整查询：

SELECT node.category_tree_id,
       node.category_id,
       cat.name,
       node.lft,
       node.rgt,
       (Count(parent.category_tree_id) - ( sub_tree.depth + 1 )) AS depth,
       node.created_at,
       node.updated_at,
       node.updated_by
FROM   category_tree AS node
       JOIN category cat
         ON cat.category_id = node.category_id,
       category_tree AS parent,
       category_tree AS sub_parent,
       (SELECT node.category_tree_id,
               ( Count(parent.category_tree_id) - 1) AS depth
        FROM   category_tree AS node,
               category_tree AS parent
        WHERE  node.lft BETWEEN parent.lft AND parent.rgt
               AND node.category_tree_id = 'f47f6269-9605-459e-a319-2b0177f9f4d0'
        GROUP  BY node.category_tree_id
        ORDER  BY node.lft) AS sub_tree
WHERE  (node.lft BETWEEN parent.lft AND parent.rgt)
       AND (node.lft BETWEEN sub_parent.lft AND sub_parent.rgt)
       AND (sub_parent.category_tree_id = sub_tree.category_tree_id)
GROUP  BY node.category_tree_id,
          depth,
          cat.name
HAVING (Count(parent.category_tree_id) - ( sub_tree.depth + 1 )) <= 1
ORDER  BY node.lft

为什么在我的嵌套集合层次结构中我的 HAVING 子句没有正确比较 int 值？

Why in my nested set hierarchy is my HAVING clause not comparing int values properly?

mysql

postgresql

nested-sets

categories