的MySQL - 顯示記錄對一個記錄

Question

我有一個表中的以下數據：

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 

該數據按時間順序使用日期時間字段排序。我想顯示這些記錄「對」爲1行，像這樣：

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 

有幾個需要注意的地方：如果沒有類型1開始，然後顯示在結果表Type1Km場NULL。同樣，如果沒有Type2結束，則在記錄的Type2Km字段中顯示NULL。

我怎麼能這樣做？

Answer 1

不幸的是，MySQL的缺乏FULL OUTER JOIN，所以你必須要UNION兩套在一起。

這將讓你在哪兒Type1Km存在，Type2Km是否確實的情況。

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 

現在我們需要Type1Km不存在的情況。

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那些在一起，你所期望的結果：

(
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

在我以前的查詢，我忘了考慮有一個「2型「記錄在一開始。更新爲解釋這一點。這裏的結果我得到：

數據在times表：

+----------+------+------------+ 
| 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 | 
+----------+------+------------+ 

查詢的結果：

+-----------+---------+---------+ 
| 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

如果可以的話，改變你的表結構有一個type1km和type2km，然後或者在添加公里時更新，或者在選擇時總結。

Answer 3

這可能會實現

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'); 

我按小時假設組，也沒什麼看頭你的榜樣結果是不準確的

爲了更好地解釋這一有趣查詢做什麼

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