Question

我在一个表格中有以下数据：

Time, Type, Kilometers
12:00, 1, 0.1
12:30, 2, 0.2
14:00, 1, 0.4
15:00, 2, 1.0
16:00, 1, 1.2
16:30, 2, 1.5
16:45, 1, 2.0

此数据使用DateTime字段按时间顺序排序。我想将这些记录“对”显示为1行，如下所示：

StartTime, Type1Km, Type2Km
12:00, 0.1, 0.2
14:00, 0.4, 1.0
16:00, 1.2, 1.5
16:45, 2.0, NULL

有几点需要注意：如果没有Type1启动，则在结果表的Type1Km字段中显示NULL。同样，如果没有Type2结束，则在记录的Type2Km字段中显示NULL。

我怎么能这样做？

Answer 1

不幸的是，MySQL缺少FULL OUTER JOIN，因此您必须将UNION两个集合在一起。

这将为您提供Type1Km存在的情况，无论Type2Km是否存在。

SELECT
    t1.`Time` as StartTime,
    t1.`Kilometers` as Type1Km,
    t2.`Kilometers` as Type2Km
FROM `times` t1
LEFT JOIN `times` t2 ON t2.`Type` = 2
                    AND t2.`Time` = (SELECT `Time` FROM `times`
                                     WHERE `Time` > t1.`Time`
                                     ORDER BY `Time` LIMIT 1)
WHERE t1.`Type` = 1

现在我们需要Type1Km不存在的情况。

SELECT
    t2.`Time` as StartTime,
    NULL as Type1Km,
    t2.`Kilometers` as Type2Km
FROM `times` t2
LEFT JOIN `times` t1 ON t1.`Time` = (SELECT `Time` FROM `times`
                                     WHERE `Time` < t2.`Time`
                                     ORDER BY `Time` DESC LIMIT 1)
WHERE t2.`Type` = 2
  AND (t1.`Type` = 2 OR t1.`Type` IS NULL)

UNION这些人在一起，你得到了理想的结果：

(
SELECT
    t1.`Time` as StartTime,
    t1.`Kilometers` as Type1Km,
    t2.`Kilometers` as Type2Km
FROM `times` t1
LEFT JOIN `times` t2 ON t2.`Type` = 2
                    AND t2.`Time` = (SELECT `Time` FROM `times`
                                     WHERE `Time` > t1.`Time`
                                     ORDER BY `Time` LIMIT 1)
WHERE t1.`Type` = 1

) UNION ALL (

SELECT
    t2.`Time` as StartTime,
    NULL as Type1Km,
    t2.`Kilometers` as Type2Km
FROM `times` t2
LEFT JOIN `times` t1 ON t1.`Time` = (SELECT `Time` FROM `times`
                                     WHERE `Time` < t2.`Time`
                                     ORDER BY `Time` DESC LIMIT 1)
WHERE t2.`Type` = 2
  AND (t1.`Type` = 2 OR t1.`Type` IS NULL)
)

ORDER BY `StartTime`

更新

在我之前的查询中，我忘记了在一开始就记录了“2型”记录。更新以解释该问题。这是我得到的结果：

times表中的数据：

+----------+------+------------+
| Time     | Type | Kilometers |
+----------+------+------------+
| 11:00:00 |    2 |        0.1 |
| 12:00:00 |    1 |        0.1 |
| 12:30:00 |    2 |        0.2 |
| 14:00:00 |    1 |        0.4 |
| 14:30:00 |    1 |        0.8 |
| 15:00:00 |    2 |        1.0 |
| 15:30:00 |    2 |        0.2 |
| 16:00:00 |    1 |        1.2 |
| 16:30:00 |    2 |        1.5 |
| 16:45:00 |    1 |        2.0 |
+----------+------+------------+

查询结果：

+-----------+---------+---------+
| StartTime | Type1Km | Type2Km |
+-----------+---------+---------+
| 11:00:00  |    NULL |     0.1 |
| 12:00:00  |     0.1 |     0.2 |
| 14:00:00  |     0.4 |    NULL |
| 14:30:00  |     0.8 |     1.0 |
| 15:30:00  |    NULL |     0.2 |
| 16:00:00  |     1.2 |     1.5 |
| 16:45:00  |     2.0 |    NULL |
+-----------+---------+---------+

Answer 2

如果可以，将表结构更改为type1km和type2km，然后在添加kms时更新或在选择时总结。

Answer 3

这可能有效

select 
max(Time), 
substring_index(group_concat(if(type=2,null,Kilometers) order by type),',',1),
substring_index(group_concat(if(type=1,null,Kilometers) order by type desc),',',1) 
from your_table 
group by date_format(Time, '%H');

我按小时假设小组，也不值得你的例子结果不准确

更好地解释搞笑查询的内容

group_concat(if(type=2,null,Kilometers) order by type
-- this is ensure the Kilometers must NOT from type=2

group_concat(if(type=1,null,Kilometers) order by type desc
-- this is ensure the Kilometers must NOT from type=1

MySQL - 在一条记录中显示记录对

3 个答案: