笔试面试 Mysql中表student_table(id,name,birth,sex),插入如下记录: (‘1004’ , ‘张三’ , ‘2000-08-06’ , ‘男’); (‘1005’ , NULL , ‘2001-12-01’ , ‘女’); (‘1006’ , ‘张三’ , ‘2000-08-06’ , ‘女’); (‘1007’ , ‘王五’ , ‘2001-12-01’ , ‘男’); (‘1008’ , ‘李四’ , NULL, ‘女’); (‘1009’ , ‘李四’ , NULL, ‘男’); (‘1010’ , ‘李四’ , ‘2001-12-01’, ‘女’); 执行 select count(t1.birth) as c1 from ( select * from student_table where sex = ‘男’ ) t1 right join (select * from student_table where sex = ‘女’) t2 on t1.birth = t2.birth and t1.name = t2.name ; 的结果行数是()?