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I have written a query:

SELECT TimeStamp, FwdHr, W FROM Meter_Data 
WHERE TimeStamp Between 1356908255 AND 1356944255 
OR (TimeStamp BETWEEN 1356911855 AND 1356947855) 
OR (TimeStamp BETWEEN 1356915455 AND 1356951455) 
OR (TimeStamp BETWEEN 1356919055 AND 1356955055) 
OR (TimeStamp BETWEEN 1356922655 AND 1356958655) 
AND MeterID = @meterID 
AND DeviceID = @deviceID 
ORDER BY TimeStamp

but problem is that it returns multiple records for every between clause but i just want one. LIMIT will limit total records = 1 for whole query. so cannot use that. please help!

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2 回答 2

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在 MySQL 中，您可以使用变量来执行此操作。这是一种方法：

SELECT TimeStamp, FwdHr, W
FROM (select md.*, 
             (case when TimeStamp Between 1356908255 AND 1356944255 then @rn1 := @rn1 + 1
                   when TimeStamp BETWEEN 1356911855 AND 1356947855 then @rn2 := @rn2 + 1
                   when TimeStamp BETWEEN 1356915455 AND 1356951455 then @rn3 := @rn3 + 1
                   when TimeStamp BETWEEN 1356919055 AND 1356955055 then @rn4 := @rn4 + 1
                   when TimeStamp BETWEEN 1356922655 AND 1356958655 then @rn5 := @rn5 + 1
              end) as rn
      from Meter_Data cross join
           (select @rn1 := 0, @rn2 := 0, @rn3 := 0, @rn4 := 0, @rn5 := 0) const
      WHERE MeterID = @meterID AND DeviceID = @deviceID 
     ) md
where rn = 1
ORDER BY TimeStamp;

这为每个组定义了一个单独的变量。然后它在看到时增加变量，在rn“列”中返回结果。这只是选择遇到的第一个值。

于 2013-06-04T13:18:15.073 回答
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使用一系列 UNIONed 查询：-

(SELECT TimeStamp, FwdHr, W 
FROM Meter_Data 
WHERE TimeStamp Between 1356908255 AND 1356944255 
AND MeterID = @meterID
AND DeviceID = @deviceID 
ORDER BY TimeStamp
LIMIT 1)
UNION
(SELECT TimeStamp, FwdHr, W 
FROM Meter_Data 
WHERE TimeStamp BETWEEN 1356911855 AND 1356947855
AND MeterID = @meterID 
AND DeviceID =     @deviceID 
ORDER BY TimeStamp
LIMIT 1)
UNION
(SELECT TimeStamp, FwdHr, W 
FROM Meter_Data 
WHERE TimeStamp BETWEEN 1356915455 AND 1356951455
AND MeterID = @meterID 
AND DeviceID =     @deviceID 
ORDER BY TimeStamp
LIMIT 1)
UNION
(SELECT TimeStamp, FwdHr, W 
FROM Meter_Data 
WHERE TimeStamp BETWEEN 1356919055 AND 1356955055
AND MeterID = @meterID 
AND DeviceID =     @deviceID 
ORDER BY TimeStamp
LIMIT 1)
UNION
(SELECT TimeStamp, FwdHr, W 
FROM Meter_Data 
WHERE TimeStamp BETWEEN 1356922655 AND 1356958655
AND MeterID = @meterID 
AND DeviceID =     @deviceID 
ORDER BY TimeStamp
LIMIT 1)

您可能需要更改参数名称并根据您的数据库类多次传递它们

另一种可能性（但未经测试）是有一个子选择来获取仪表 ID/设备 ID 的每个范围内的最大时间戳，添加一个 CASE 语句来获取一行是哪个范围并按此分组，然后将结果加入反对主表。

请注意，如果仪表 ID/设备 ID 组合存在重复的时间戳，则这将无法正常工作。

不知道这会更快还是更慢！

SELECT Meter_Data.TimeStamp, Meter_Data.FwdHr, Meter_Data.W 
FROM Meter_Data 
INNER JOIN (SELECT MAX(TimeStamp) AS MaxTimestamp, MeterID, DeviceID,
CASE 
    WHEN TimeStamp Between 1356908255 AND 1356944255 THEN 1
    WHEN TimeStamp BETWEEN 1356911855 AND 1356947855 THEN 2
    WHEN TimeStamp BETWEEN 1356915455 AND 1356951455 THEN 3
    WHEN TimeStamp BETWEEN 1356919055 AND 1356955055 THEN 4
    WHEN TimeStamp BETWEEN 1356922655 AND 1356958655 THEN 5
END AS GroupNo
FROM Meter_Data 
WHERE (TimeStamp Between 1356908255 AND 1356944255 
OR TimeStamp BETWEEN 1356911855 AND 1356947855
OR TimeStamp BETWEEN 1356915455 AND 1356951455
OR TimeStamp BETWEEN 1356919055 AND 1356955055
OR TimeStamp BETWEEN 1356922655 AND 1356958655) 
AND MeterID = @meterID 
AND DeviceID = @deviceID 
GROUP BY MeterID, DeviceID, GroupNo) Sub1
ON Meter_Data.MeterID = Sub1.MeterID
AND Meter_Data.DeviceID = Sub1.DeviceID
AND Meter_Data.TimeStamp = Sub1.MaxTimestamp
ORDER BY Meter_Data.TimeStamp
于 2013-06-04T11:56:35.173 回答