数据库实验5

一、查询会计1201班所有学生信息

FROM t_class a
INNER JOIN t_student b ON a.cls_id=b.cls_id
WHERE a.cls_name ='会计1201'

二、查询所有班级的男女生人数以及男女比例

  a.cls_name,
  SUM(CASE WHEN b.stu_gender=1 THEN 1 ELSE 0 END) male,
  SUM(CASE WHEN b.stu_gender=2 THEN 1 ELSE 0 END) female,
  SUM(CASE WHEN b.stu_gender=1 THEN 1 ELSE 0 END)/SUM(CASE WHEN b.stu_gender=2 THEN 1 ELSE 0 END)
FROM t_class a
INNER JOIN t_student b ON a.cls_id=b.cls_id
GROUP BY a.cls_name