select isnull(a.mydata,0)-isnull(b.mydata,0) from a,b where a.datatime=b.datatime order by a.datatime
既然要按时间排列,那么select中的列就要有datatime这个字段,否则会出错 我觉得应该这样写:SELECT (a.mydata-b.mydata) as mydata , a.datatime FROM a , b WHERE a.datatime = b.datatime ORDER BY a.datatime
我觉得应该这样写:SELECT (a.mydata-b.mydata) as mydata , a.datatime
FROM a , b
WHERE a.datatime = b.datatime
ORDER BY a.datatime