Question

我有一个（游戏）排行榜表，其中包含一个由另一个查询更新的排名。它以ID为中心 - 当我查询表格时，我理想地想要获取N条记录。所以我在记录上做了一个UNION，其限制为N / 2，如下所示：

(SELECT * FROM test1 t WHERE t.rank > (SELECT rank FROM test1 t2 WHERE id=ID)+0 ORDER BY rank LIMIT 0, N/2)
UNION ALL
(SELECT * FROM test1 t WHERE t.rank <= (SELECT rank FROM test1 t2 WHERE id=ID)+0 ORDER BY rank desc LIMIT 0, N/2) ORDER BY rank

虽然在排行榜的顶部时这不起作用，但它只会返回较低的N / 2。有没有办法确保它总能返回N条记录？我确实认为你可以故意获得比所需更多的记录，然后修剪你不需要的记录。虽然我不知道怎么用查询来做这个！

任何帮助表示赞赏：）

Answer 1

您可以巧妙地使用order by和limit：

来执行此操作

SELECT t.*
FROM test1 t cross join
     (SELECT rank FROM test1 t2 WHERE id = @ID) as theone
ORDER BY ABS(theone.rank - t.rank)
LIMIT N;

然后你可能希望这些按顺序排列：

SELECT t.*
FROM (SELECT t.*
      FROM test1 t cross join
           (SELECT rank FROM test1 t2 WHERE id = @ID) as theone
      ORDER BY ABS(theone.rank - t.rank)
      LIMIT N
     ) t
ORDER BY t.rank;

Answer 2

尝试以下方法：

(SELECT * FROM test1 t WHERE t.rank > (SELECT rank FROM test1 t2 WHERE id=ID)+0 ORDER BY rank LIMIT 0,N)
UNION ALL
(SELECT * FROM test1 t WHERE t.rank <= (SELECT rank FROM test1 t2 WHERE id=ID)+0 ORDER BY rank desc LIMIT 0,N)
ORDER BY rank
LIMIT 0,N

有关详情，请参阅manual。

确保从MySQL查询返回正确的行数

2 个答案: