mysql - 如何解决这个 MySQL 查询？

Question

我有一个如下所示的表格:

    CREATE TEMPORARY TABLE MainList (
  `pTime` int(10) unsigned NOT NULL,
  `STD` double NOT NULL,
  PRIMARY KEY (`pTime`)
) ENGINE=MEMORY;


+------------+-------------+
| pTime      | STD         |
+------------+-------------+
| 1106080500 |  -0.5058072 |
| 1106081100 | -0.82790455 |
| 1106081400 | -0.59226294 |
| 1106081700 | -0.99998194 |
| 1106540100 | -0.86649279 |
| 1107194700 |  1.51340543 |
| 1107305700 |  0.96225296 |
| 1107306300 |  0.53937716 |
+------------+-------------+ .. etc

pTime 是我的主键。

我想要进行一个查询，对于表中的每一行，将找到第一个 pTime，其中 STD 具有翻转的符号，并且比上表的 STD 距离 0 更远。 (为简单起见，假设我正在寻找 0-STD)

这是我想要的输出示例:

+------------+-------------+------------+-------------+
| pTime      | STD         | pTime_Oppo | STD_Oppo    |
+------------+-------------+------------+-------------+
| 1106080500 |  -0.5058072 | 1106090400 |  0.57510881 |
| 1106081100 | -0.82790455 | 1106091300 |  0.85599817 |
| 1106081400 | -0.59226294 | 1106091300 |  0.85599817 |
| 1106081700 | -0.99998194 | 1106091600 |  1.0660959  |
+------------+-------------+------------+-------------+

我似乎无法理解它! 我尝试了以下方法:

SELECT DISTINCT
    MainList.pTime,
    MainList.STD,
    b34d1.pTime,
    b34d1.STD
FROM
    MainList
JOIN b34d1 ON(
    b34d1.pTime > MainList.pTime
    AND(
        (
            MainList.STD > 0
            AND b34d1.STD <= 0 - MainList.STD
        )
        OR(
            MainList.STD < 0
            AND b34d1.STD >= 0 - MainList.STD
        )
    )
);

该代码只会卡住我的服务器。

P.S 表 b34d1 就像 MainList 一样，只是它包含更多元素:

mysql>  select STD, Slope from b31d1 limit 10;
+-------------+--------------+
| STD         | Slope        |
+-------------+--------------+
| -0.44922675 |   -5.2016129 |
| -0.11892021 |  -8.15249267 |
|  0.62574686 | -10.19794721 |
|  1.10469057 | -12.43768328 |
|  1.52917352 | -13.08651026 |
|  1.61803899 |  -13.2441349 |
|  1.82686555 | -12.04912023 |
|  2.07480736 | -11.22067449 |
|  2.45529961 |  -7.84090909 |
|  1.86468335 |  -6.26466276 |
+-------------+--------------+
mysql>  select count(*) from b31d1;
+----------+
| count(*) |
+----------+
|   439340 |
+----------+

一组 1 行(0.00 秒)

事实上 MainList 只是使用 MEMORY 引擎的 b34d1 的过滤版本

mysql> show create table b34d1;
+-------+-----------------------------------------------------------------------------------------------
-------------------------------------------------------------------------------------------------------+
| Table | Create Table
                                                                                                       |
+-------+-----------------------------------------------------------------------------------------------
-------------------------------------------------------------------------------------------------------+
| b34d1 | CREATE TABLE `b34d1` (
  `pTime` int(10) unsigned NOT NULL,
  `Slope` double NOT NULL,
  `STD` double NOT NULL,
  PRIMARY KEY (`pTime`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 MIN_ROWS=339331 MAX_ROWS=539331 PACK_KEYS=1 ROW_FORMAT=FIXED |
+-------+-----------------------------------------------------------------------------------------------
-------------------------------------------------------------------------------------------------------+

编辑:我刚刚做了一个小实验，结果让我很困惑:

SELECT DISTINCT
    b34d1.pTime,
    b34d1.STD,
    Anti.pTime,
    Anti.STD

FROM
    b34d1

LEFT JOIN b34d1 As Anti ON(
    Anti.pTime > b34d1.pTime
    AND(
        (
            b34d1.STD > 0
            AND b34d1.STD <= 0 - Anti.STD
        )
        OR(
            b34d1.STD < 0
            AND b34d1.STD >= 0 - Anti.STD
        )
    )
)  limit 10;

+------------+-------------+------------+------------+
| pTime      | STD         | pTime      | STD        |
+------------+-------------+------------+------------+
| 1104537600 | -0.70381962 | 1104539100 | 0.73473692 |
| 1104537600 | -0.70381962 | 1104714000 | 1.46733274 |
| 1104537600 | -0.70381962 | 1104714300 | 2.02097356 |
| 1104537600 | -0.70381962 | 1104714600 | 2.60642099 |
| 1104537600 | -0.70381962 | 1104714900 | 2.01006557 |
| 1104537600 | -0.70381962 | 1104715200 | 1.97724189 |
| 1104537600 | -0.70381962 | 1104715500 | 1.85683704 |
| 1104537600 | -0.70381962 | 1104715800 |  1.2754127 |
| 1104537600 | -0.70381962 | 1104716100 | 0.87900156 |
| 1104537600 | -0.70381962 | 1104716400 | 0.72957739 |
+------------+-------------+------------+------------+

为什么第一个pTime下的所有值都相同？

Answer 1

在 SQL 中，从具有某些聚合统计信息(例如最小值或最大值)的行中选择其他字段有点困惑。这样的查询并不那么简单。您通常需要额外的联接或子查询。例如:

SELECT m.pTime, m.STD, m2.pTime AS pTime_Oppo, m2.STD AS STD_Oppo
  FROM MainList AS m
    JOIN 
      (SELECT m1.pTime, MIN(m2.pTime) AS pTime_Oppo
         FROM MainList AS m1
           JOIN MainList AS m2 
             ON m1.pTime < m2.pTime AND SIGN(m1.STD) != SIGN(m2.STD)
         WHERE ABS(m1.STD) <= ABS(m2.std)
         GROUP BY m1.pTime
      ) AS oppo ON m.pTime = oppo.pTime
    JOIN MainList AS m2 ON oppo.pTime_Oppo = m2.pTime
;

使用示例数据:

INSERT INTO MainList (`pTime`, `STD`)
  VALUES
(1106080500, -0.5058072),
(1106081100, -0.82790455),
(1106081400, -0.59226294),
(1106081700, -0.99998194),
(1106090400,  0.57510881),
(1106091300,  0.85599817),
(1106091600,  1.0660959),
(1106540100, -0.86649279),
(1107194700,  1.51340543),
(1107305700,  0.96225296),
(1107306300,  0.53937716),
;

结果是:

+------------+-------------+------------+-------------+
| pTime      | STD         | pTime_Oppo | STD_Oppo    |
+------------+-------------+------------+-------------+
| 1106080500 |  -0.5058072 | 1106090400 |  0.57510881 |
| 1106081100 | -0.82790455 | 1106091300 |  0.85599817 |
| 1106081400 | -0.59226294 | 1106091300 |  0.85599817 |
| 1106081700 | -0.99998194 | 1106091600 |   1.0660959 |
| 1106090400 |  0.57510881 | 1106540100 | -0.86649279 |
| 1106091300 |  0.85599817 | 1106540100 | -0.86649279 |
| 1106540100 | -0.86649279 | 1107194700 |  1.51340543 |
+------------+-------------+------------+-------------+