如何從結果集中獲取最小計數，最大計數和總結果集計數

我需要從結果集中獲取最小計數，最大計數和總結果集計數。執行查詢後，它會產生多行，我需要從中提取數據。例如查詢：如何從結果集中獲取最小計數，最大計數和總結果集計數

SELECT count(*) AS `countTotal`,`admission_no`,`course` FROM `attendance` WHERE `course` = '15' AND `timestamp` AND `admission_no` !='0' AND `timestamp` BETWEEN '2016-04-01 00:00:00.0' AND '2017-03-31 00:00:00.0' GROUP BY `admission_no` ORDER BY `countTotal` DESC

OUT PUT

countTotal admission_no course 
4   2304    15 
4   2442    15 
3   2777    15 
2   2967    15 
2   3288    15

我嘗試這樣做：

if (overallTotalClassRow.next()) { 
    maxclassaverage = overallTotalClassRow.getInt(1); 
}

但是這會給最大值。即4.

我需要得到4和2作爲最大值和最小值，總計數爲5.我怎麼能這樣..任何幫助將不勝感激。

來源

2016-12-23 Karthik CP

'和時間戳' 將永遠是正確的。見http://meta.stackoverflow.com/questions/333952/why-should-i-provide-an-mcve-for-what-seems-to-me-to-be-a-very-simple-sql-query – Strawberry

@Strawberry也許他正在檢查時間戳不爲空。 – JonahCui

試試這個。

 select min(countTotal) as MinCount ,max(countTotal) as MaxCount, 
     count(*) as totalCount from 
     (SELECT count(*) AS `countTotal`,`admission_no`,`course` 
     FROM `attendance` WHERE `course` = '15' AND `timestamp` 
     AND `admission_no` !='0' AND `timestamp` 
     BETWEEN '2016-04-01 00:00:00.0' AND '2017-03-31 00:00:00.0' 
     GROUP BY `admission_no` 
     )a

然後用

來源

2016-12-23 08:21:54

錯誤顯示：每個派生表必須有自己的別名 –

哇！它像魅力一樣工作..最簡單的方法，而不是從Java ..非常感謝 –

最受歡迎@KarthikCP –

的Java方法： -

1）將countTotal在一個ArrayList
2）使用Collections類最大值和最小值的方法來找到最大值和最小值。例如： -

Comparator<String> comparator = new Comparator<String>() { 
     @Override 
     public int compare(String o1, String o2) { 
      return Integer.valueOf(o1).compareTo(Integer.valueOf(o2)); 
     } 
    }; 
int max=Collections.max(list, comparator);

3）ArrayList.size（）來查找總計數。

SQL方法： -

使用最大值，最小值和總數的查詢工會。

來源

2016-12-23 08:21:28

我認爲最簡單的方法是：

int maximum = 0; 
int minimum =0; 
int totalCount =0; 

if (overallTotalClassRow.next()) { 
    totalCount +=1; 
    if(totalCount ==1) { 
     maximum = overallTotalClassRow.getInt(1); 
     minimum = overallTotalClassRow.getInt(1); 
    } 
    if (overallTotalClassRow.getInt(1)> maximum) { 
     maximum = overallTotalClassRow.getInt(1); 
    } 
    if (overallTotalClassRow.getInt(1)< maximum) { 
     minimum = overallTotalClassRow.getInt(1); 
    } 
}

來源

2016-12-23 08:24:10 JonahCui

如何從結果集中獲取最小計數，最大計數和總結果集計數

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