mysql全外和交叉&&sql92pksql99

 #全外
 use girls;
 SELECT b.*,a.*
 FROM beauty b
 FULL OUTER JOIN boys a
 on b.boyfrien_id=a.id;

 #交叉连接99标准笛卡尔乘积
 SELECT b.*,ob.*
 FROM beauty b
 CROSS JOIN boys ob;

 #sql92和sql99pk
 #功能：sql99支持的较多
 #可读性：sql99实现连接条件和筛选条件分离，可读性较高

 #一、查询编号>3的女神的男朋友信息，如果有则列出详细，如果没有，用nu11填充、
 SELECT b.id,b.name,be.*
 FROM beauty b
 LEFT OUTER JOIN boys be
 ON b.boyfriend_id=be.id
 and b.id>3;

 #二、查询哪个城市没有部门
 USE myemployees;
 SELECT city
 FROM locations l
 LEFT OUTER JOIN departments d
 on d.location_id=l.location_id
 WHERE d.department_id is null;

 #三、查询部门名为SAM或IT的员工信息
 SELECT e.*,d.department_name
 FROM employees e
 LEFT OUTER JOIN departments d
 on e.department_id=d.department_id
 WHERE d.department_name in('SAL','IT');