Question

以下查询准确地返回值w.price但是w.time被赋予2017-11-23 15:12:00，这不是返回行中的正确值。但是，它始终与WHERE time >=子句匹配。造成这种情况的原因是什么？

SELECT
    history.pair_id,
    MIN(history.price) as all_time_low,
    history.time as all_time_low_time,
    w.price as one_week_price,
    w.time as one_week_time
    FROM ep_ex_waex history

INNER JOIN (
    SELECT MIN(price) as price, time, pair_id
    FROM ep_ex_waex
    WHERE pair_id = 2
    AND time >= '2017-11-23 15:12:00'
) as w ON w.pair_id = history.pair_id

结果

+---------+--------------+---------------------+----------------+---------------------+
| pair_id | all_time_low | all_time_low_time   | one_week_price | one_week_time       |
+---------+--------------+---------------------+----------------+---------------------+
| 2       | 392.3        | 2017-11-23 12:11:00 | 396.77         | 2017-11-23 15:12:00 |
+---------+--------------+---------------------+----------------+---------------------+

列all_time_low_time不正确。

ep_ex_waex结构

CREATE TABLE `ep_ex_waex` (
  `id` int(11) NOT NULL,
  `pair_id` int(11) DEFAULT NULL,
  `price` double NOT NULL,
  `volume` double NOT NULL,
  `time` datetime NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

Answer 1

也许这个mod会关注结果，使用WHERE来定位基于pair_id和MIN的价格。

SELECT price, time, pair_id
   FROM  ep_ex_waex ep 
   WHERE pair_id = 2
   AND time >= '2017-11-23 15:12:00'
   AND price = (SELECT min(price) FROM ep_ex_waex WHERE pair_id=ep.pair_id);

您的完整查询如下所示：

SELECT
  history.pair_id,
  MIN(history.price) as all_time_low,
  history.time as all_time_low_time,
  w.price as one_week_price,
  w.time as one_week_time
  FROM ep_ex_waex history

INNER JOIN (
  SELECT price, time, pair_id
  FROM ep_ex_waex ep
  WHERE pair_id = 2
  AND time >= '2017-11-23 15:12:00'
  AND price = (SELECT MIN(price) FROM ep_ex_waex eps WHERE eps.pair_id=ep.pair_id)
) as w ON w.pair_id = history.pair_id;

如果不使用这么多的subqueris，它可能会被优化很多，但希望你能得到这个想法。

祝你好运。

=== TEST CASE === 使用的数据：

+-------+---------------------+---------+
| price | time                | pair_id |
+-------+---------------------+---------+
|  1.29 | 2017-11-23 15:12:00 |       2 |
|  1.19 | 2017-11-24 15:12:00 |       2 |
|  1.79 | 2017-11-25 15:12:00 |       2 |
+-------+---------------------+---------+

查询：

mysql-sql>     SELECT price, time, pair_id
        FROM ep_ex_waex ep
        WHERE pair_id = 2
        AND time >= '2017-11-23 15:12:00'
        AND price = (SELECT MIN(price) FROM ep_ex_waex eps WHERE eps.pair_id=ep.pair_id);

+-------+---------------------+---------+
| price | time                | pair_id |
+-------+---------------------+---------+
|  1.19 | 2017-11-24 15:12:00 |       2 |
+-------+---------------------+---------+

看起来对我来说，找到了中间记录，最低价格和匹配日期。将您的查询分解为细分，看看是否可以使其正常工作。

WHERE子句覆盖字段值

1 个答案: