Question

这些是我正在使用的创建表：

create table Customer2 (cid char(3), cname char(10), primary key (Cid)); 

create table Employee2 
(
     eid char(3), ename char(10), salary number(7,2), 
     mid char(3), 
     primary key (eid), foreign key (mid) references Employee2
); 

create table ArtObject2 
(
      aoid char(3), atitle char(12), artist varchar(10), pricea number(8,2), 
      primary key (aoid)
); 

create table MakesD2 
(
     aoid char(3), eid char(3), cid char(3), prices number, dates date, 
     primary key (aoid, CID), 
     foreign key (aoid) references ArtObject2, 
     foreign key (CID) references Customer2, 
     foreign key (eid) references Employee2
);

我需要编写以下SQL语句：

找到购买数量最多的客户的名字。
查找在1-JUL-12之后购买多件油画的客户
为每幅画卖出展示画作的标题，由客户支付的价格和＃34;高于平均水平＆＃34;如果这幅画的售价高于平均要价和“低于平均水平”的话。如果这幅画是出售的价格低于平均要价。对于包含单词＆＃34;高于的列问＆＃34;或者＆＃34;低于要求＆＃34;标题备注。

我为＃1尝试了这个声明，但没有奏效：

select cname 
from customer2 
where cid in 
      (select cid 
       from makesd2 
       where prices >=ALL(select prices from makesd2 group by cname)
      );

我为＃2尝试了这个声明但没有返回所有结果：

select cname 
from customer2 
where cid in
      (select cid 
       from makesd2 
       where dates > '1-JUL-12' 
       group by cid 
       having count(cid) > 1);

任何帮助将不胜感激。感谢

Answer 1

1：您必须制作子查询以获取每个客户购买的绘画数量，并使用customer2表格加入以获取客户的姓名：

SELECT c.cname
FROM Customer2 c
INNER JOIN (
  SELECT cid,
    COUNT(*) AS bought
  FROM makesd2
  GROUP BY cid
  ) m ON m.cid = c.cid
ORDER BY m.bought

2：与上面相同，但是在这一篇中，你会发现自那个日期以来买了不止一幅画的cid是什么：

SELECT c.cname
FROM Customer2 c
INNER JOIN (
  SELECT cid,
    COUNT(*) AS bought
  FROM makesd2
  WHERE dates > '1-JUL-12'
  GROUP BY cid
  HAVING COUNT(*) > 1
  ) m ON m.cid = c.cid

3：这个是CASE的简单用法：

SELECT a.atitle,
  m.prices,
  CASE 
    WHEN m.aprice > (SELECT AVG(prices) FROM MakesD2)
      THEN 'Higher than average'
    ELSE 'Lower than average'
  END AS averageRating
FROM MakesD2 m
INNER JOIN ArtObject2 a ON a.aoid = m.aoid

SQL Select语句查询

1 个答案: