SQL query to find employee with 3 year over year salary raises?

Question

Here is the table. My initial observation would be to query the salary to which employee has an incremental salary per year, but am confused on how to do that. Employee 1 is the only employee that has a three year increase, but not sure how to single them out. Thanks!

Answer 1

You can do this using lead() / lag() and aggregation:

select employee_id
from (select t.*,
             lag(salary) over (partition by employee_id order by year) as prev_salary
      from t
     ) t
group by employee_id
having min(salary - prev_salary) > 0 and
       count(*) = 3;

This compares salaries in adjacent years and returns employees where the value is always increasing. It assumes that there are no gaps in the years -- as in your sample data.

The advantage of this approach is that you don't need to know the years in advance.

Answer 2

One option uses aggregation:

select employee_id
from mytable t
group by employee_id
having max(salary) filter(where year = 2020) > max(salary) filter(where year = 2019)
   and max(salary) filter(where year = 2019) > max(salary) filter(where year = 2018)

This brings employee whose 2020 salary is greather than their 2019 salary, and whose 2019 salary is greater than their 2018 salary - which is how I understood your question.

Answer 3

I guess you don't want to hardcode the years in your query.
The best choice is the use of the window function LAG() to get the salary of the previous 2 years, but you should also check that the 3 years that you check are consecutive:

SELECT DISTINCT employee_id
FROM (
  SELECT *, 
    LAG(year, 1) OVER (PARTITION BY employee_id ORDER BY year) year1,
    LAG(salary, 1) OVER (PARTITION BY employee_id ORDER BY year) salary1,
    LAG(year, 2) OVER (PARTITION BY employee_id ORDER BY year) year2,
    LAG(salary, 2) OVER (PARTITION BY employee_id ORDER BY year) salary2 
  FROM tablename t
)
WHERE year1 = year - 1 AND year2 = year - 2 AND salary > salary1 AND salary1 > salary2 

If you want to check only for the current year and the 2 previous years then add 1 more condition in the WHERE clause:

...AND year = strftime('%Y', CURRENT_DATE) 

so you don't need to hardcode the current year,