MySQL GROUP BY期末

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我正在嘗試將「值」列分組到4小時的結束時間段（上午4點，上午8點，下午12點）。我正在使用MySQL版本5.7。MySQL GROUP BY期末

一個實例表和數據是如下：

CREATE TABLE TestData(
    Timestamp DATETIME, 
    Value FLOAT 
); 


INSERT INTO TestData 
(Timestamp, Value) 
VALUES 
('2017-08-15 00:00:00', RAND()), 
('2017-08-15 00:15:00', RAND()), 
('2017-08-15 00:30:00', RAND()), 
('2017-08-15 00:45:00', RAND()), 
('2017-08-15 01:00:00', RAND()), 
('2017-08-15 01:15:00', RAND()), 
('2017-08-15 01:30:00', RAND()), 
('2017-08-15 01:45:00', RAND()), 
('2017-08-15 02:00:00', RAND()), 
('2017-08-15 02:15:00', RAND()), 
('2017-08-15 02:30:00', RAND()), 
('2017-08-15 02:45:00', RAND()), 
('2017-08-15 03:00:00', RAND()), 
('2017-08-15 03:15:00', RAND()), 
('2017-08-15 03:30:00', RAND()), 
('2017-08-15 03:45:00', RAND()), 
('2017-08-15 04:00:00', RAND()), 
('2017-08-15 04:15:00', RAND()), 
('2017-08-15 04:30:00', RAND()), 
('2017-08-15 04:45:00', RAND()), 
('2017-08-15 05:00:00', RAND()), 
('2017-08-15 05:15:00', RAND()), 
('2017-08-15 05:30:00', RAND()), 
('2017-08-15 05:45:00', RAND()), 
('2017-08-15 06:00:00', RAND()), 
('2017-08-15 06:15:00', RAND()), 
('2017-08-15 06:30:00', RAND()), 
('2017-08-15 06:45:00', RAND()), 
('2017-08-15 07:00:00', RAND()), 
('2017-08-15 07:15:00', RAND()), 
('2017-08-15 07:30:00', RAND()), 
('2017-08-15 07:45:00', RAND()), 
('2017-08-15 08:00:00', RAND()), 
('2017-08-15 08:15:00', RAND()), 
('2017-08-15 08:30:00', RAND()), 
('2017-08-15 08:45:00', RAND()), 
('2017-08-15 09:00:00', RAND()), 
('2017-08-15 09:15:00', RAND()), 
('2017-08-15 09:30:00', RAND()), 
('2017-08-15 09:45:00', RAND()), 
('2017-08-15 10:00:00', RAND()), 
('2017-08-15 10:15:00', RAND()), 
('2017-08-15 10:30:00', RAND()), 
('2017-08-15 10:45:00', RAND()), 
('2017-08-15 11:00:00', RAND()), 
('2017-08-15 11:15:00', RAND()), 
('2017-08-15 11:30:00', RAND()), 
('2017-08-15 11:45:00', RAND()), 
('2017-08-15 12:00:00', RAND()), 
('2017-08-15 12:15:00', RAND()), 
('2017-08-15 12:30:00', RAND()), 
('2017-08-15 12:45:00', RAND()), 
('2017-08-15 12:45:00', RAND());

我要舍入到下一個時間段（因此使用大於）。當我運行以下查詢：

SELECT 
    Timestamp, 
    ROUND(AVG(Value), 3) AS Value 
FROM 
    TestData 
WHERE 
    Timestamp > '2017-08-15 00:00:00' AND Timestamp <= '2017-08-15 12:00:00' 
GROUP BY 
    UNIX_TIMESTAMP(Timestamp) DIV 14400; -- 14400 seconds = 4 hours

這將返回：

+---------------------+-------+ 
| Timestamp   | Value | 
+---------------------+-------+ 
| 2017-08-15 00:15:00 | 0.244 | 
| 2017-08-15 01:00:00 | 0.478 | 
| 2017-08-15 05:00:00 | 0.439 | 
| 2017-08-15 09:00:00 | 0.499 | 
+---------------------+-------+ 
4 rows in set (0.00 sec)

我想什麼：

+---------------------+-------+ 
| Timestamp   | Value | 
+---------------------+-------+ 
| 2017-08-15 04:00:00 | 0.244 | 
| 2017-08-15 08:00:00 | 0.478 | 
| 2017-08-15 12:00:00 | 0.439 | 
+---------------------+-------+ 
3 rows in set (0.00 sec)

可能有人請讓我知道這怎麼可能？

謝謝。

來源

2017-08-15 Conrad M

如果我的RAND值不匹配你的嗎？這不是很有用，是嗎？ – Strawberry

這些值本身並不重要 - 只要組平均值是正確的 –

查詢

SELECT 
    TIMESTAMP 
    , ROUND(AVG(VALUE), 3) AS VALUE 
FROM 
testdata 
WHERE 
    HOUR(TIMESTAMP) >= 4 
AND 
    HOUR(TIMESTAMP) <= 12 
GROUP BY 
FLOOR(HOUR(TIMESTAMP)/4)

結果

timestamp    Value 
------------------- -------- 
2017-08-15 04:00:00  0.500 
2017-08-15 08:00:00  0.441 
2017-08-15 12:00:00  0.527

來源

2017-08-15 11:30:48

請注意，這實際上會返回TIMESTAMP的不確定值（如果您使用CEILING替換FLOOR時可以進行演示） - 但它可能不會實質性影響結果。 – Strawberry

MySQL GROUP BY期末

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