如果类别不是无限嵌套的，则可以一次将它们加入一个级别。以下是最多3个嵌套级别的示例：
SELECt c.name, COUNT(DISTINCT p.PID) as postCount FROM categories AS c LEFT JOIN categories AS c2 ON c2.parent = c.catidLEFT JOIN categories AS c3 ON c3.parent = c2.catidLEFT JOIN posts AS p ON c.CATID = p.category OR c2.CATID = p.category OR c3.CATID = p.categoryWHERe c.parent = '0' GROUP BY c.CATID, c.nameORDER BY c.name ASC
