MySQL 5.7 - 使用最早创建的 child 更新 parent 记录

Question

我的目标是创建一个 UPDATE 语句来更新 parent 记录的 default_page_id 成为最早 child 创建的记录。

parent/child是2级max/deep受UI限制； parent_id 列表示记录的 parent，root 的 type 值进一步简化了 root/parents 的内容。

我有一个带 DDL/DML 的 dbfiddle：https://dbfiddle.uk/?rdbms=mysql_5.7&fiddle=994d9bf3b20b3bbab21547d4334fc0e7

最终我的 SELECT 会变成我的 UPDATE is here but uses MIN(id) wouldn't be feasible as id is a char(36) 因此 id 不会自动递增；我已尝试使用 MIN(created)，但缺少对 GROUP BY 的必要更新以解决此问题，希望能多多关注！

SELECT
    *
FROM
    (
        SELECT
            test_pages.id
        FROM
            test_pages
        WHERE
            test_pages.default_page_id is null
        and test_pages.type = "root"
    ) as a
LEFT JOIN(
    SELECT
        parent_id ,
        MIN(id) AS id
    from
        test_pages
    WHERE
        test_pages.type = "container"
    GROUP BY
        parent_id
) as b ON b.parent_id = a.id

Answer 1

SQL (SELECT):

如果我对问题的理解正确，以下 sql 可能会有所帮助：

SELECT
    r.id,
    r.default_page_id,
    r.type,
    r.title,
    c.parent_id AS container_parent_id,
    c.id AS container_id
FROM
    test_pages AS r
    LEFT JOIN (
        SELECT
            parent_id,
            id
        FROM
            test_pages
        WHERE
            type = "container"
            AND created = (
                SELECT
                    MIN(created)
                FROM
                    test_pages AS tp
                WHERE
                    type = "container"
                    AND test_pages.parent_id = tp.parent_id
            )
    ) AS c ON r.id = c.parent_id
WHERE
    type = "root";

SQL（更新）：

更新sql如下：

UPDATE
    test_pages AS t
SET
    t.default_page_id = (
        SELECT
            id
        FROM
            (
                SELECT
                    parent_id,
                    id
                FROM
                    test_pages
                WHERE
                    type = "container"
                    AND created = (
                        SELECT
                            MIN(created)
                        FROM
                            test_pages AS tp
                        WHERE
                            type = "container"
                            AND test_pages.parent_id = tp.parent_id
                    )
            ) AS c
        WHERE
            t.id = c.parent_id
    );

输出：

更新后，test_pages 如下所示 table：

id	version_id	parent_id	default_page_id	type	title	created	modified
jf2039jf932032f	2	abc1212312efff	nan	container	Child Page 2	2022-02-23 23:25:41	nan
7eajiefaeiaeaeleailje	2	nan	8efjaliejfaelfjael	root	Root Page A	nan	nan
8efjaliejfaelfjael	2	7eajiefaeiaeaeleailje	nan	container	Child Page Again 1	2022-02-04 23:26:01	nan
abc1212312efff	2	nan	ejejejejejej	root	Root Page	nan	nan
ejejejejejej	2	abc1212312efff	nan	container	Child Page 1	2022-02-03 23:26:01	nan
fefeee9f9e9fee	2	nan	nan	root	Root Page With No Children	nan	nan
jklfjealkjlfajfl	2	7eajiefaeiaeaeleailje	nan	container	Child Page Again 2	2022-02-07 23:25:41	nan

注：

如果同一父容器下有多个id不同但created完全相同的容器，可能会报错如下。在这种情况下，您必须编写额外的代码。所以请小心。

Query 1: Subquery returns more than 1 row

MySQL 5.7 - 使用最早创建的 child 更新 parent 记录

MySQL 5.7 - Update parent records with oldest created child

mysql

sql

mysql-5.7

SQL (SELECT):

SQL（更新）：

输出：

注：