java - 如何从结果集中获取最小计数、最大计数和总结果集计数

Question

我需要从结果集中获取最小计数、最大计数和总结果集计数。执行查询后，它会产生多行，我需要从中提取数据。 例如查询:

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

输出

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

我试过这个:

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

但这会给出最大值。即 4.

我需要得到 4 和 2 作为最大值和最小值，总计数为 5。我该怎么做......任何帮助将不胜感激。

Answer 1

试试这个。

        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

然后使用