DELETE 递归 PostgreSQL 尊重特定条件

Question

几天前，我问了一个关于从 PostgreSQL 中删除 using WITH RECURSIVE 的问题。有：

效果很好：最初的目的是递归删除父文件夹，只要最后一个子文件夹被删除。下图更好地描述了它：

Files tree view

通过删除文件5.jpg，在这种情况下，所有父文件夹也将被删除。

但现在我必须删除父文件夹 只有当它们变空时 ，即失去唯一的子文件夹。我尝试了以下方法：

 WITH RECURSIVE all_uploads (codigo, parent, ext, uploader) AS (
    SELECT ut1.codigo, ut1.codigo_upload_temp_pai AS parent, ut1.codigo_extensao AS ext, ut1.codigo_usuario_inclusao AS uploader
    FROM upload_temp ut1
    WHERE ut1.codigo = 576

    UNION ALL

    SELECT ut2.codigo, ut2.codigo_upload_temp_pai AS parent, ut2.codigo_extensao AS ext, ut2.codigo_upload_temp_pai AS uploader
    FROM upload_temp ut2
    JOIN all_uploads au ON au.parent = ut2.codigo
    WHERE (SELECT ut3.codigo FROM upload_temp ut3 WHERE ut3.codigo_upload_temp_pai = ut2.codigo LIMIT 1) IS NULL
    AND ext IS NULL
    AND uploader = 1535
 )
 DELETE FROM upload_temp WHERE codigo IN (SELECT codigo FROM all_uploads);

我认为检查文件夹是否为空的唯一方法是执行子select 考虑到自我关系。如果SELECT ut3.codigo FROM upload_temp ut3 WHERE ut3.codigo_upload_temp_pai = ut2.codigo LIMIT 1) IS NULL returns true，那么文件夹是空的。通过使用自引用功能（文件夹和文件相同的数据库 table），我通过检查 codigo_extensao 字段知道它是一个文件夹（只有文件有扩展名）。

好吧，它不起作用，它只删除了我的 5.jpg。有什么提示吗？提前致谢！

Answer 1

您不能随心所欲地递归删除。这里的逻辑是创建一个查询来删除你想要的所有内容，然后运行它递归地直到有更多要删除的内容。

这是一个完全满足您需要的函数：

CREATE OR REPLACE FUNCTION p_remove_empty_folders(_codigo_usuario_ integer) RETURNS integer AS $$
DECLARE
    AFFECTEDROWS integer;
BEGIN

    WITH a AS (
    DELETE FROM upload_temp WHERE codigo IN (SELECT ut1.codigo FROM upload_temp ut1 WHERE ut1.codigo_usuario_inclusao = _codigo_usuario_ AND ut1.codigo_extensao IS NULL AND NOT EXISTS (SELECT * FROM upload_temp ut2 WHERE ut2.codigo_upload_temp_pai = ut1.codigo)) 
    RETURNING 1
    )
    SELECT count(*) INTO AFFECTEDROWS FROM a;    

    WHILE AFFECTEDROWS > 0 LOOP

        WITH a AS (
        DELETE FROM upload_temp WHERE codigo IN (SELECT ut1.codigo FROM upload_temp ut1 WHERE ut1.codigo_usuario_inclusao = _codigo_usuario_ AND ut1.codigo_extensao IS NULL AND NOT EXISTS (SELECT * FROM upload_temp ut2 WHERE ut2.codigo_upload_temp_pai = ut1.codigo)) 
        RETURNING 1
        )
        SELECT count(*) INTO AFFECTEDROWS FROM a;

    END LOOP;

    RETURN 0;
END;
$$ LANGUAGE plpgsql;

再见！

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