Question

问题：如何在不排除其他时间跨度的相关数据的情况下，如何采用下面的查询并忽略结果中可能为负的任何时间跨度？（换句话说，我不能把条件放在WHERE子句中，因为Timespan1和2可能是好的，但timepan3是负的，但我想保留它们。

我是否在AVG功能中放置了一个case语句？有没有更有效的方法来运行它？

    SELECT DATE(tbl.time1) AS 'date',
          AVG((time_to_sec(timediff(tbl.time2 , tbl.time1))/3600) ) AS 'avg_time1',
          AVG((time_to_sec(timediff(tbl.time3 , tbl.time2))/3600) ) AS 'avg_time2',
          AVG((time_to_sec(timediff(tbl.time4 , tbl.time3))/3600) ) AS 'avg_time3',
    FROM tbl
    WHERE DATE(tbl.time1) = '$variable'
    GROUP BY DATE(tbl.time1)

我发现它使用了重复的Alex提到的原则：

SELECT AVG(`a`), AVG(IF(`b` > -1, `b`, NULL)), AVG(`c`) FROM `t`;

Answer 1

我认为您希望使用HAVING关键字？

SELECT DATE(tbl.time1) AS 'date',
          AVG((time_to_sec(timediff(tbl.time2 , tbl.time1))/3600) ) AS 'avg_time1',
          AVG((time_to_sec(timediff(tbl.time3 , tbl.time2))/3600) ) AS 'avg_time2',
          AVG((time_to_sec(timediff(tbl.time4 , tbl.time3))/3600) ) AS 'avg_time3',
    FROM tbl
    WHERE 
        AND DATE(tbl.time1) = '$variable'
    GROUP BY DATE(tbl.time1) 
    HAVING avg_time1 > 0 AND avg_time2 > 0 and avg_time3 > 0;

Answer 2

您可以使用case声明执行此操作：

SELECT DATE(tbl.time1) AS "date",
       (CASE WHEN AVG(time_to_sec(timediff(tbl.time2 , tbl.time1))/3600) >= 0
             THEN AVG(time_to_sec(timediff(tbl.time2 , tbl.time1))/3600)
        END) as avg_time1,
       (CASE WHEN AVG(time_to_sec(timediff(tbl.time3 , tbl.time2))/3600) >= 0
             THEN AVG(time_to_sec(timediff(tbl.time3 , tbl.time2))/3600) 
        END) as avg_time2,
       (CASE WHEN AVG(time_to_sec(timediff(tbl.time4 , tbl.time3))/3600) >= 0
             THEN AVG(time_to_sec(timediff(tbl.time4 , tbl.time3))/3600)
        END) as avg_time3
FROM tbl
WHERE DATE(tbl.time1) = '$variable'
GROUP BY DATE(tbl.time1);

这将返回NULL值而不是负值，这正是我猜你想要的。

此外，您应该仅对日期和字符串文字值使用单引号，而不是对标识符（例如列名称）使用单引号。虽然MySQL允许这种语法，但使用它通常会导致混淆。

PHP Mysql计算日期时间之间的平均值，并忽略平均值的负面结果

2 个答案: