mysql>-- 笛卡尔积查询,无连接条件查询
mysql>select a.*,b.* from customers a , orders b ;

mysql>-- 内连接,查询符合条件的记录.
mysql>select a.*,b.* from customers a , orders b where a.id = b.cid ;

mysql>-- 左外连接,查询符合条件的记录.
mysql>select a.*,b.* from customers a left outer join orders b on a.id = b.cid ;

mysql>-- 右外连接,查询符合条件的记录.
mysql>select a.*,b.* from customers a right outer join orders b on a.id = b.cid ;

mysql>-- 全外连接,查询符合条件的记录(mysql不支持全外链接)
mysql>select a.*,b.* from customers a full outer join orders b on a.id = b.cid ;