select a.*,b.*,c.* from a inner join b on a.a1 = b.b1 left join c on a.a2 = c.c2 where a.a1='xx' 主要用标准sql的inner join ,left join ,right join 进行连接,左连,右连; on 后面可以加括号,加其他条件,也可以用括号来确定先连接哪个再连接哪个
select School.SchoolID,Student.StudentName from School full join Class on School.ClassId=Class.ClassId full join Student on Class.StudentId=Student.StudentId 要查找的东西放在最上面,然后连接表,连接条件。就这样。
第2个回答 2019-05-16
select School.SchoolID,Student.StudentNamefrom Student left join Class on Student.StudentId = Class.Student left join School on Class.ClassId = School.ClassId