Grouping in PostgreSQL?

Question

PostgreSQL

There is a table:

id| country | salary
1 | sweden | 3000
2 | germany| 3900
3 | sweden | 3500
4 | sweden | 29005
| germany| 3300

Required:

1. get records with maximum salary values ​​in each of the countries
   
2. get the id of those posts
   

Expected result:
id | country | salary
3 | sweden | 3500
2 | germany| 3900

Which query to use to achieve this result?

query: returns error: column "t.id" must appear in a GROUP BY clause or be used in an aggregate function
SELECT id, max(salary) FROM t GROUP BY country;

Answer 1

SELECT t.id, t.country, t.salary 
  FROM t
    INNER JOIN 
      ( SELECT country, max(salary) AS max_salary FROM t GROUP BY country ) tm
        ON t.country = tm.country AND t.salary = tm.max_salary

Checking .