Question

我的网站上有一种Facebook式的喜欢/不喜欢的系统，并使用以下查询来获取特定帖子的喜欢和不喜欢：

SELECT DISTINCT * FROM posts WHERE cid='$cid' AND pid=".implode(" OR pid=",$pids)." ORDER BY time DESC

$pid是要搜索的帖子ID数组。

zbid是当前正在访问该页面的用户的ID。现在，如果该用户对该帖子进行了评分（喜欢/不喜欢），则应首先返回其结果，然后在该订单之后按time DESC排序结果。

如何修改查询以执行此操作？

如果posts表包含以下数据：

+----+-----+------+-----+--------+------+
| id | cid | zbid | pid | rating | time |
+----+-----+------+-----+--------+------+
| 1  | 1   | 1    | 1   | 1      | 1    |
+----+-----+------+-----+--------+------+
| 2  | 1   | 2    | 1   | -1     | 4    |
+----+-----+------+-----+--------+------+
| 3  | 1   | 3    | 2   | 1      | 2    |
+----+-----+------+-----+--------+------+
| 4  | 2   | 4    | 1   | -1     | 3    |
+----+-----+------+-----+--------+------+
| 5  | 1   | 5    | 1   | 1      | 8    |
+----+-----+------+-----+--------+------+
| 6  | 1   | 6    | 1   | -1     | 7    |
+----+-----+------+-----+--------+------+

当前的select语句（上面）将返回以下信息（使用$pid = array(1);）：

+----+-----+------+-----+--------+------+
| id | cid | zbid | pid | rating | time |
+----+-----+------+-----+--------+------+
| 5  | 1   | 5    | 1   | 1      | 8    |
+----+-----+------+-----+--------+------+
| 6  | 1   | 6    | 1   | -1     | 7    |
+----+-----+------+-----+--------+------+
| 2  | 1   | 2    | 1   | -1     | 4    |
+----+-----+------+-----+--------+------+
| 4  | 2   | 4    | 1   | -1     | 3    |
+----+-----+------+-----+--------+------+
| 1  | 1   | 1    | 1   | 1      | 1    |
+----+-----+------+-----+--------+------+

但是，如果zbid=4的用户正在访问该网页，则应该将该结果（如果存在）提升到顶部，如下所示：

+----+-----+------+-----+--------+------+
| id | cid | zbid | pid | rating | time |
+----+-----+------+-----+--------+------+
| 4  | 2   | 4    | 1   | -1     | 3    |
+----+-----+------+-----+--------+------+
| 5  | 1   | 5    | 1   | 1      | 8    |
+----+-----+------+-----+--------+------+
| 6  | 1   | 6    | 1   | -1     | 7    |
+----+-----+------+-----+--------+------+
| 2  | 1   | 2    | 1   | -1     | 4    |
+----+-----+------+-----+--------+------+
| 1  | 1   | 1    | 1   | 1      | 1    |
+----+-----+------+-----+--------+------+

变量$zbid设置为正在访问该页面的用户zbid。

Answer 1

使用您提供的信息，这是一个相当粗略的解决方案：

解决方案1 - 便携式方式

-- This query will return User's posts and give it a higher priority in ordering, via post_order field
SELECT 
  posts.*
  ,0 as post_order
FROM posts
WHERE
  (cid='$cid' AND pid=".implode(" OR pid=",$pids).") AND
  (zbid = $user_zbid)

UNION ALL

-- This query will return everything BUT User's posts and give it a lower priority in ordering
SELECT 
  posts.*
  ,1 as post_order
FROM posts
WHERE
  (cid='$cid' AND pid=".implode(" OR pid=",$pids).") AND
  (zbid <> $user_zbid)
ORDER BY
  post_order -- This clause will put User's posts before the others
  ,time DESC

解决方案2 - 效果更佳的方式（建议的cbranch信用额度）

SELECT 
  posts.*
  ,IF(zbid = $user_zbid, 0, 1) as post_order
FROM posts
WHERE
  (cid='$cid' AND pid=".implode(" OR pid=",$pids).")
ORDER BY
  post_order -- This clause will put User's posts before the others
  ,time DESC

备注
- 你可能已经注意到了，我从SELECT中删除了DISTINCT，因为我看不出它们的原因。由于您只是从单个表中提取数据，因此您不应该有重复项。显然，您仍然可以添加它们，但请记住不要使用此类条款，除非确实需要它 - 第二个查询运行起来非常昂贵，因为它使用＆＃34;不等于＆＃34;条款。这意味着它不会使用索引，并且它不适合大量数据。如果您必须处理大表，则必须审查此解决方案。

Answer 2

在回顾迭戈的建议后，我想出了以下有效的答案：

SELECT zbid,pid,rating,0 as post_order,time
    FROM posts
    WHERE cid='$cid'
        AND (pid=".implode(" OR pid=",$pids).")
        AND zbid!='$zbid'
UNION
SELECT zbid,pid,rating,1 as post_order,time
    FROM posts
    WHERE cid='$cid'
        AND (pid=".implode(" OR pid=",$pids).")
        AND zbid='$zbid'
ORDER BY
    post_order DESC,
    time DESC

如何使用2个不同的ORDER BY语句形成MySQL查询

2 个答案: