如果是mysql的话可以使用字符串拼接函数concat:
insert into tab1 (startdateandtime) select concat(startdate, time) as satartdateandtime from tab2;
我来回答,
insert into 表1 select convert(datetime,convert(nvarchar(20),startdate)+convert(nvarchar(20),[time])) from 表2
insert into 表1 (startdateandtime) select startdate||time from 表2
insert into 表1 (startdateandtime) select startdate+time from 表2