计算1列中最后2条记录之间的差异

Question

我试图找到列中最后2个值之间的差异。 这是我想要实现的目标;

Select abs(water1-water2)/60
from (select dec_pw_water_reset from timer_table order by desc limit 1 as water1) t1
join
(select dec_pw_water_reset from timer_table order by desc limit 1,1 as water2) t2

Answer 1

假设您有一个自动递增id列，您可以在select中使用两个子查询：

select abs(
    (select dec_pw_water_reset from timer_table order by id desc limit 1) -
    (select dec_pw_water_reset from timer_table order by id desc limit 1, 1)
    ) / 60 as diff;

根据您的需要调整order by子句。

Demo on rextester