[MySQL相关]内联，左外联，右外联，全连接，交叉连接 的区别

典型多对多联表查询:

select man_to_women.nid,man.name as mname, women.name as wname from man_to_women  
left join man on man_to_women.man_id = man.nid
left join women on man_to_women.women_id = women.nid
where man.name = 'alex'

左联:显示左边表的所有数据,只显示右边表与左边表有关联的数据