SQL - Avg value by year

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');

For the above data I am trying to determine the average sales considering only year. For example the data as only 2 years, so the average is total/2. One way of doing is may get distinct years & total sum from subquery and then average. I am exploring if there is a better way of doing it. Any pointers are helpful. Thanks in advance.

user_10676716 · Answer

Do you just want aggregation?

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

This produces one row per year, with the average value of salesamt.

On the other hand, if you want the average of yearly sales, then you can use two levels of aggregation:

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

I think the query you had in mind was:

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

It produces the same result as the second query. You would need to test both queries against your data to see which performs better.

user_10004574 · Answer

select year(salesdate) as yearofsales , avg(salesamt) as salesavg from sales group by year(salesdate) order by yearofsales

SQL - Avg value by year

2 Answers