内连接：

select name, depart_name, city
from employee e join department d
on e.depart_id = d.depart_id
join location l
on d.locat_id = l.locat_id;

外连接

 注：本图取自博客园大佬"anliux"的博客，原帖链接：【学习总结】SQL的连接：join -- 内连接外连接左连接右连接 - anliux - 博客园

最下边两种查询情况需要用关键字"union all"进行连表，这里以左边满外连接为例：

select ......
from 表1 as a
left join 表2 as b
on a.列名 = b.列名
union all
select ......
from 表1 as a
right join 表2 as b
on a.列名 = b.列名
where a.列名 is null