select a.username ,b.schoolname,c.classname from user a
 left out join schoolTable b on a.school =b.id
 left out join classTable c on a.class=c.id

------解决方案--------------------

select a.id as '学员编号',a.username as '学生姓名',b.schoolname as '学校',c.classname as '班级' from user a
left join school b on a.id = b.id
left join class c on c.id = a.id

dgv.datasource = dataset.tables[0];

------解决方案--------------------

探讨


引用:

SQL code
select a.username ,b.schoolname,c.classname from user a
left out join schoolTable b on a.school =b.id
left out join classTable c on a.class=c.id


返回一个DataTable，然后dataG……


------解决方案--------------------
数据精准的话你用inner join都会差不多。当然，这要看要不要这么严谨的数据库结构了。