選擇項的第一次出現在最後的分組

Question

混亂，但是，這裏的情況：

我們已經有了對應於一個地方坐鎮程序以1個分鐘的間隔序列號。

Sequence# | Timestamp 
    1  | 2012-04-11 12:00:00 
    2  | 2012-04-11 12:01:00 
    2  | 2012-04-11 12:02:00 
    2  | 2012-04-11 12:03:00 
    3  | 2012-04-11 12:04:00 
    5  | 2012-04-11 12:05:00 
    5  | 2012-04-11 12:06:00 
    6  | 2012-04-11 12:07:00 
    1  | 2012-04-11 12:08:00 
    2  | 2012-04-11 12:09:00 
    2  | 2012-04-11 12:10:00 
    2  | 2012-04-11 12:11:00 
    3  | 2012-04-11 12:12:00 

的序列的持續時間可以改變，但間隔始終是相同的（每1分鐘精確）。

正如你所看到的，序列重複。 我如何才能找到Seqence n的最新開始發帖？

所以，如果我想搜索序列2，我希望回到2 | 2012-04-11 12:09:00因爲它是序列的最新，啓動次數2

Answer 1

嘗試：

SELECT t1.* FROM `table_name` t1 
LEFT JOIN `table_name` t2 
on t1.`Sequence` = t2.`Sequence` and 
    t1.`Timestamp` = t2.`Timestamp` + interval 1 minute 
WHERE t1.`Sequence`=2 and t2.`Sequence` is null 
ORDER BY t1.`Timestamp` DESC LIMIT 1 

SQLFiddle here。

Answer 2

我想這是你想要的...

SELECT * FROM `table_name` WHERE `Sequence`=2 ORDER BY `Timestamp` DESC LIMIT 1 

Answer 3

這是你想要的嗎？

$desired_sequence=2; 

$query="SELECT * FROM `table_name` ORDER BY `Timestamp` DESC"; 
$result = mysql_query($query); 
if (mysql_errno()) { die("ERROR ".mysql_errno($link) . ": " . mysql_error($link)); } 

$found_desired=0; 
while($row = mysql_fetch_array($result)) 
{ 
    if($row['Sequence']==$desired_sequence) 
    { 
     $found_desired=1; 
     $timestamp=$row['Timestamp']; 
    } 

    if(($found_desired==1) && ($row['Sequence']!=$desired_sequence)) 
    { 
     return; // End the while loop because $timestamp will have your desired output. 
    } 
} 

Answer 4

我不確定你到底在這裏。我寫了一些代碼，如果數據在文本文件中，這些代碼就可以工作。如果數據在數據庫中，則會更容易。不過，我從你的例子中假設你有| |分離它不在數據庫中的數據。

function findLastOccurenceOfSequence ($sequenceNumber) 
{ 
    if (@!is_int ($sequenceNumber)) 
     throw new Exception ("Expected param1 to be an integer"); 
    $data = file_get_contents ("testFile.txt"); 
    $dataArray = explode ("\n", $data); 
    $dataArray = array_reverse ($dataArray); 
    $returnLine = ""; 
    $sequenceStarted = false; 
    foreach ($dataArray as $key => &$dataLine) 
    { 
     $pieces = explode ("|", $dataLine); 
     if (count ($pieces) != 2) 
      continue; 
     list ($thisSequenceNum, $timeStamp) = $pieces; 
     $thisSequenceNum = intval (trim ($thisSequenceNum)); 
     if ($thisSequenceNum == $sequenceNumber) 
     { 
      $sequenceStarted = true; 
      $returnLine = $dataLine; 
     } 
     else if ($sequenceStarted) 
     { 
      break; 
     } 
    } 

    if ($key == count ($dataArray)) 
    { 
     throw new Exception ("Sequence not found!"); 
    } 

    return $returnLine; 
} 

echo "OCCURRENCE: " . findLastOccurenceOfSequence (2);