我如何申請限制這個父/子樹如表查詢

Question

這裏的表結構：

CREATE TABLE `message` (
    `id` int(11) NOT NULL AUTO_INCREMENT, 
    `uid` int(11) NOT NULL, 
    `from_uid` int(11) NOT NULL, 
    `content` varchar(300) NOT NULL, 
    `parent` int(11) DEFAULT NULL, 
    `create_time` datetime NOT NULL, 
    PRIMARY KEY (`id`), 
    KEY `uid` (`uid`), 
    KEY `from_uid` (`from_uid`), 
    KEY `parent` (`parent`), 
    CONSTRAINT `message_ibfk_1` FOREIGN KEY (`uid`) REFERENCES `u 
ser` (`id`) ON DELETE CASCADE ON UPDATE CASCADE, 
    CONSTRAINT `message_ibfk_2` FOREIGN KEY (`from`) REFERENCES `user 
` (`id`) ON DELETE CASCADE ON UPDATE CASCADE, 
    CONSTRAINT `message_ibfk_3` FOREIGN KEY (`parent`) REFERENCES `message` (`id`) ON DELETE CASCADE ON UPDATE CASCADE 
) ENGINE=InnoDB AUTO_INCREMENT=20 DEFAULT CHARSET=utf8 | 

這是一個表來存儲用戶的郵件和答覆。如果我對整個查詢應用一個限制，讓我們假設限制爲30，則結果將是包含父消息和子消息（答覆）的30行。但是，如何獲得每條消息的回覆30條父消息？

Answer 1

試試這個：

SELECT `message`.* 
FROM 
     `message` INNER JOIN 
     (SELECT `id` FROM `message` WHERE `parent` IS NULL LIMIT 30) `ids` ON 
      `message`.`id` = `ids`.`id` OR `message`.`parent` = `ids`.`id`