建表语句：
time = take(10:10:00.300+1..30*300, 200) tradeMoney = double(take(1..100, 200)) SecurityId = take(`A, 100) join take(`B, 100) volume = take(1..300, 200) t = table(time,tradeMoney, SecurityId,volume)
表结构如下：
想取一天内time最早和最晚时间的volume差值，group by SecurityID。请问在dolphindb中怎么写好呢？
可以尝试这样写：
select last(volume) - first(volume) from t group by SecurityId
结果如下：
