上次我们介绍了：SQL Server实践性练习之子查询实例，本文我们主要介绍一些SQL Server实践性练习的一些高级SQL查询的实例，接下来就让我们来一起了解一下这部分内容。
--3.6.2 检索没有通过代理商a05订货的所有顾客的名字
- select cname from customers except
- (select cname from customers,orders where customers.cid=orders.cid and orders.aid='a05')
--这时except是关键
---3.6.3 检索对同一产品至少订购了两次的所有顾客的名字
- select cname from customers where cid in
- (select cid from orders group by cid,pid having count(pid)>=2)
--答案:
- select distinct cname from (select o.cid as spcid from orders o,orders x where o.cid=x.cid
- and o.pid=x.pid and o.ordno<> x.ordno)y, customers c where y.spcid=c.cid;
--3.6.4 检索至少订购了一件价格低于￥0.50 的商品的所有顾客的姓名
--答案:我没做出来,下面这种方法运行没通过
select distinct cname from (orders join products using(pid)) join customers using(cid) where price<0.50
--法2:将3个表直接连接起来就可以了
select distinct cname from (orders o join products p on o.pid=p.pid) join customers c on o.cid=c.cid where p.price<0.5
--3.7.1 求出所有订货交易的总金额
select sum(dollars) as totaldollars from orders;
--3.7.2 求出产品p03的订购总量
select pid,count(pid) as 订购总量 from orders where pid='p03' group by pid --错误的，没理解题意
--答案：
select sum(qty) as total from orders where pid='p03'
--3.7.3 求出顾客总数的查询
select count(*) as 顾客总数 from customers
--3.7.4 求出有顾客居住的城市的数目
select count(distinct city) as 有顾客居住的城市数目 from customers
--3.7.5 列出折扣值小于***折扣值的所有顾客的cid值
- select cid,cname,discnt from customers where discnt<
- (select max(discnt) from customers)
--实际上那条空值的记录没有选进来
--3.7.6 找出至少被两个顾客订购的所有产品（可以推广到多于两个顾客的情况）
select pid from orders group by pid having count(cid)>=2
--我的思路是 select pid from orders
--select pid,count(cid) as 产品被几个顾客订购 from orders group by pid having count(cid)>=2
--答案如下：
select p.pid from products p where 2<=(select count(distinct cid) from orders where pid=p.pid)
--3.7.7
insert into customers (cid,cname,city)
values ('c009','Windix','Dallas');
select * from customers where discnt<=10 or discnt>10
--显然,没有查出所有记录
--使用特殊谓词is null
select * from customers where discnt is null or discnt<=10 or discnt>10
--3.8 SQL中行的分组
--3.8.1 创建一个计算每样产品被每个代理商订购的总量的查询
select aid,pid,sum(qty) as 每个代理商订购的总量 from orders group by aid,pid
3、执行效率的分析
--题4：找出订购了产品p05的顾客的名字
select cname from customers where cid in (select cid from orders where pid='p05')
--答案用最直接的SQL语句来解决该查询问题
select distinct cname from customers,orders where customers.cid = orders.cid and orders.pid='p05';
--用连接也能达到相同的效果，重要的是拆解题目的意思
select distinct cname from customers inner join orders on customers.cid = orders.cid and orders.pid='p05';
--那么我们来看一下三种情况的执行效率
- SET ANSI_NULLS ON
- GO
- SET QUOTED_IDENTIFIER ON
- GO
- -- =============================================
- -- Author:<Author,,Name>
- -- Create date: <Create Date,,>
- -- Description:<Description,,>
- -- =============================================
- alter PROCEDURE a
- @pid varchar(10)
- AS
- BEGIN
- --select cname from customers where cid in (select cid from orders where pid=@pid) 16ms
- --select distinct cname from customers,orders where customers.cid = orders.cid and orders.pid=@pid; 3ms
- --select distinct cname from customers inner join orders on customers.cid = orders.cid and orders.pid=@pid; 3ms
- END
- GO
- DBCC FREEPROCCACHE --清除缓存，以免下次计算时间
- declare @begin datetime
- declare @End datetime
- set @begin=getdate()
- exec a 'p05'
- set @End=getdate()
- select datediff(ms,@begin,@End) as 执行时间(毫秒)
--由此可见，一般情况下这种题目能直接写的就直接用连接的方法，用in的效率极低。
关于SQL Server数据库实践性练习之高级SQL查询的实例介绍就到这里了，希望本次的介绍能够对您有所帮助。
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