SQL

Question

create table sales(
  invoiceid int primary key,
  deptid int, 
  salesamt decimal(10,2),
  salesdate datetime
  );
  
insert into sales values (101, 2, 2111.02, '20160102');
insert into sales values (102, 2, 421.00, '20160202');
insert into sales values (103, 2, 675.00, '20160202');
insert into sales values (104, 2, 4355.00, '20160302');
insert into sales values (105, 2, 975.00, '20160304');
insert into sales values (106, 2, 1021.00, '20160402');
insert into sales values (107, 2, 2106.00, '20160425');
insert into sales values (108, 2, 2799.81, '20160501');
insert into sales values (109, 2, 4335.75, '20160502');
insert into sales values (110, 2, 12006.00, '20160521');
insert into sales values (111, 2, 5220.00, '20160602');
insert into sales values (112, 2, 7198.02, '20160618');
insert into sales values (113, 2, 4795.00, '20160625');
insert into sales values (114, 2, 5341.00, '20160706');
insert into sales values (115, 2, 5795.00, '20160718');
insert into sales values (116, 2, 6400.00, '20160725');
insert into sales values (117, 2, 14795.00, '20160812');
insert into sales values (118, 2, 43395.00, '20160825');
insert into sales values (119, 2, 47595.00, '20160914');
insert into sales values (120, 2, 46795.00, '20160930');
insert into sales values (121, 2, 6223.00, '20161010');
insert into sales values (122, 2, 7702.00, '20161012');
insert into sales values (123, 2, 11292.00, '20161107');
insert into sales values (124, 2, 33211.00, '20161126');
insert into sales values (125, 2, 16430.00, '20161206');
insert into sales values (126, 2, 87010.00, '20161221');
insert into sales values (127, 2, 2111.02, '20170102');
insert into sales values (128, 2, 421.00, '20170202');
insert into sales values (129, 2, 675.00, '20170202');
insert into sales values (130, 2, 4355.00, '20170302');
insert into sales values (131, 2, 975.00, '20170304');
insert into sales values (132, 2, 1021.00, '20170402');
insert into sales values (133, 2, 2106.00, '20170425');
insert into sales values (134, 2, 2799.81, '20170501');
insert into sales values (135, 2, 4335.75, '20170502');
insert into sales values (136, 2, 12006.00, '20170521');
insert into sales values (137, 2, 5220.00, '20170602');
insert into sales values (138, 2, 7198.02, '20170618');
insert into sales values (139, 2, 4795.00, '20170625');
insert into sales values (140, 2, 5341.00, '20170706');
insert into sales values (141, 2, 7004.00, '20170718');
insert into sales values (142, 2, 14991.00, '20170725');
insert into sales values (143, 2, 34076.00, '20170812');
insert into sales values (144, 2, 47950.00, '20170825');
insert into sales values (145, 2, 40795.00, '20170914');
insert into sales values (146, 2, 41795.00, '20170930');
insert into sales values (147, 2, 47295.00, '20171010');
insert into sales values (148, 2, 47395.00, '20171012');
insert into sales values (149, 2, 41795.00, '20171107');
insert into sales values (150, 2, 47895.00, '20161126');
insert into sales values (151, 2, 87666.00, '20161206');
insert into sales values (152, 2, 9401.00, '20161221');

对于上述数据，我试图确定仅考虑年份的平均销售额。比如数据只有2年，所以平均值是total/2。一种方法是从子查询中获取不同的年份和总和，然后取平均值。我正在探索是否有更好的方法。任何指针都是有帮助的。提前致谢。

Answer 1

你只是想要聚合吗？

select year(salesdate) salesyear, avg(salesamt) avg_sales
from sales
group by year(salesdate)
order by salesyear

每年生成一行，平均值为salesamt。

另一方面，如果您想要年销售额的平均值，则可以使用两个级别的聚合：

select avg(salesamt) yearly_avg_sales
from (select sum(salesamt) salesamt from sales group by year(salesdate)) t

我认为您想到的查询是：

select sum(salesamt) / count(distinct year(salesdate)) yearly_avg_sales
from sales

它产生与第二个查询相同的结果。您需要针对您的数据测试这两个查询，以查看哪个执行得更好。

Answer 2

select year(salesdate) 作为 yearofsales ， avg(salesamt) 作为 salesavg 从销售组按年 (salesdate) order by yearofsales

SQL - 年均值

SQL - Avg value by year

mysql

datetime

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sum