Question

Microsoft SQL Server 2008

A worker lives in some Country, and may have more than one job, with more than one salary.

I want to get the average for each country’s individual total salary.

Tables:

1) countries(country_id, name)

2) people(ssn, name,country_id)

3) jobs(ssn, job_title, salary)

[countries]

• 1, usa
• 2, germany

[people]

• 010101, John, 1
• 020202, Lee, 1
• 030303, Harry, 2

[jobs]

• 010101, teacher, 3200
• 010101, builder, 1500
• 020202, actor, 45000
• 020202, singer, 200000
• 030303, producer, 120000

Needed Query Result:

each country’s average (for each country) = sum of each worker’s total salaries) / number of workers

Country – Average Salary

• usa – 124850
• germany – 120000

Answer 1

This should work for you:

select Salary / count(c.name) AvgSalary, c.Name
from people p
inner join 
(
  select sum(salary) Salary, p.country_id
  from jobs j
  left join people p
    on j.ssn = p.ssn
  group by p.country_id
) sal
  on p.country_id = sal.country_id
left join countries c
  on p.country_id = c.country_id
group by salary, c.Name;

See SQL Fiddle with Demo