我正在尝试查询按score
排序的分页层次评论。 score
是一个整数,注释表有一个自引用的parent_id
列。
每个页面都应包含至少一个根评论,后跟其子项。如果数据集中只有一个根注释,则只返回一个页面。
因此,考虑到comments
表中的以下数据:
+----+-------+-----------+
| id | score | parent_id |
+----+-------+-----------+
| 1 | 10 | NULL |
| 2 | 5 | NULL |
| 3 | 0 | 1 |
| 4 | 6 | 2 |
| 5 | 0 | NULL |
| 6 | 30 | 1 |
| 7 | 1 | 3 |
| 8 | 0 | 4 |
| 9 | 50 | NULL |
| 10 | 2 | 2 |
+----+-------+-----------+
我希望能够SELECT * FROM comments
... LIMIT 4 OFFSET 0
并 Page 1 成为:
+----+-------+-----------+
| id | score | parent_id |
+----+-------+-----------+
| 9 | 50 | NULL |
| 1 | 10 | NULL |
| 6 | 30 | 1 |
| 3 | 0 | 1 |
+----+-------+-----------+
Page 2 :
+----+-------+-----------+
| id | score | parent_id |
+----+-------+-----------+
| 2 | 5 | NULL |
| 4 | 6 | 2 |
| 10 | 2 | 2 |
| 5 | 0 | NULL |
+----+-------+-----------+
并且 为空,因为没有根评论。
我正在使用支持闭包表,如Bill Karwin所述,因为可以使用任何注释作为根注释独立查看注释子树,这似乎是最佳解决方案。
相关表格的结构和示例数据如下:
CREATE TABLE `comments` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`score` int(11) NOT NULL,
`parent_id` int(11) unsigned DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
INSERT INTO `comments` (`id`, `score`, `parent_id`)
VALUES
(1,10,NULL),
(2,5,NULL),
(3,0,1),
(4,6,2),
(5,0,NULL),
(6,30,1),
(7,1,3),
(8,0,4),
(9,50,NULL),
(10,2,2);
CREATE TABLE `comments_closure` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`ancestor` int(11) unsigned NOT NULL,
`descendant` int(11) unsigned NOT NULL,
`depth` int(11) unsigned NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
INSERT INTO `comments_closure` (`id`, `ancestor`, `descendant`, `depth`)
VALUES
(1,1,0), (1,3,1), (1,6,1), (1,7,2),
(2,2,0), (2,4,1), (2,10,1), (2,8,2),
(3,3,0), (3,7,1),
(4,4,0), (4,8,1),
(5,5,0),
(6,6,0),
(7,7,0),
(8,8,0),
(9,9,0),
(10,10,0);
答案 0 :(得分:0)
这适用于1级深度查询:
SELECT @id_multiplier := MAX(POW(10, -(length(id) + 1))) FROM comments;
SELECT @score_multiplier := @id_multiplier * MAX(POW(10, -(length(score) + 1))) FROM comments;
SELECT c1.id
, c1.score
, c1.parent_id
FROM comments c1
LEFT JOIN comments c2
ON c1.parent_id = c2.id
WHERE c1.parent_id IS NULL
OR c1.parent_id IN
(SELECT id FROM comments WHERE parent_id IS NULL)
ORDER BY
IF(ISNULL(c1.parent_id)
, c1.score
, c2.score + (c1.parent_id * @id_multiplier) - (1-(c1.score * @score_multiplier))
) DESC