SQL 基于其他表连接同一张表

Question

我有一个 payment 表，与 dates 表和 event 表相关。我用我想要的结果进行了单独的查询：

SELECT employee_id, payment.value ADDITIONAL
FROM payment
INNER JOIN dates ON payment.date_id = dates.id
INNER JOIN event ON payment.event_id = event.id 
WHERE date = '03-2021'
    AND employee_id = 71
    AND event.number = 10015


SELECT employee_id, payment.value SALARY
FROM payment
INNER JOIN dates ON payment.date_id = dates.id
INNER JOIN event ON payment.event_id = event.id 
WHERE date = '03-2021'
    AND employee_id = 71
    AND event.number = 4096

这基本上给出了这个结果：

我想要的是这个员工在同一行的结果：

Answer 1

改成

SELECT t1.employee_id, t1.payment.additional,t2.SALARY
FROM
(SELECT employee_id, payment.additional
FROM payment
INNER JOIN dates ON payment.date_id = dates.id
INNER JOIN event ON payment.event_id = event.id 
WHERE date = '03-2021'
    AND employee_id = 71
    AND event.number = 10015) t1
    
JOIN 

(SELECT employee_id, payment.salary SALARY
FROM payment
INNER JOIN dates ON payment.date_id = dates.id
INNER JOIN event ON payment.event_id = event.id 
WHERE date = '03-2021'
    AND employee_id = 71
    AND event.number = 4096) t2
ON t1.employee_id = t2.employee_id

Answer 2

您可以使用条件聚合来做到这一点：

SELECT p.employee_id, 
       MAX(CASE WHEN e.number = 10015 THEN p.value END) additional,
       MAX(CASE WHEN e.number = 4096 THEN p.value END) salary
FROM payment p
INNER JOIN dates d ON p.date_id = d.id
INNER JOIN event e ON p.event_id = e.id 
WHERE d.date = '03-2021' AND p.employee_id = 71
  AND e.number IN (10015, 4096)
GROUP BY p.employee_id

请注意，您应该使用它们所属的表的名称/别名来限定所有列。在您的查询中，我假设 employee_id 是 payment 中的一列，date 是 dates 中的一列。