Question

 id      timing     temp    temp1   temp2   temp3
 5260     1446746934  -76     -15      4       25
    5259    1446746332  -75     -14      5      25
    5258    1446745731  -77     -15      6      25
    5257    1446734343  -71     -10      0      21

我有上面的数百个数据。数据库将获取新值并插入到新行5261.我尝试在temp列中选择前三行平均值，例如，此值为-76，-75，-77。所以平均值应该返回-76。我在SQL代码中知道错误。

SELECT avg(temp) as temperature from tempArray  order by id DESC limit 3;

Answer 1

SELECT avg(t.temp) as temperature 
              from (select temp from tempArray  order by id DESC limit 3) t;

（通过id DESC limit 3从tempArray顺序中选择temp）t ---选择表中的前三个条目，并将此表命名为't'。然后计算平均值

Answer 2

将Group by与AVG

一起使用

SELECT avg(temp) as temperature from tempArray where id 
in( SELECT * from (SELECT id temperature from tempArray order by id DESC limit 3) as t)

如何在SQL中通过id降序获得三阶的平均温度？

2 个答案: