Select on same table without subselect - sql

Question

I have payment, period and event tables. For each employee, month and year, I want to return payment.value (SALARY) and payment.value (ADDITIONAL, like a bonus) on same row, depending of event number. The event number 10015 represent the ADDITIONAL, and event number 4986 represent the SALARY.
I was able to reach my goal:
SELECT payment.employee_id EMPLOYEE_ID, payment.value SALARY,
(SELECT payment.value ADDITIONAL FROM payment
INNER JOIN period ON payment.period_id = period.id
INNER JOIN event ON payment.event_id = event.id
WHERE period.month = 7
AND period.year = 2021
AND payment.employee_id = 71
AND event.number = 10015
) ADDITIONAL
FROM payment
INNER JOIN period ON payment.period_id = period.id
INNER JOIN event ON payment.event_id = event.id
WHERE period.month = 7
AND period.year = 2021
AND payment.employee_id = 71
AND event.number = 4986
Result:
But now I'm trying to refactor my query so I don't have nested SELECTS. How can I do that?

Answer 1

You can use aggregation:
SELECT p.employee_id,
SUM(CASE WHEN e.number = 4986 THEN p.value END) as SALARY,
SUM(CASE WHEN e.number = 10015 THEN p.value END) as ADDITIONAL
FROM payment p JOIN
period pe
ON p.period_id = pe.id JOIN
event e
ON p.event_id = e.id
WHERE pe.month = 7 AND
pe.year = 2021
p.employee_id = 71 AND
e.number IN (4986, 10015)
GROUP BY p.employee_id;
Note: This is not 100% equivalent to you query, but I think it is what you want to do. This returns one row with salary and additional on one row. If there are multiple rows for the employee's salary in the period, then this returns one row whereas yours would return each row separately.