查询连续两个季度的内容

Question

我有一个名为评估的表。它有 4 列：user_id、季度、年份、内容。

我想选择连续两个季度的所有字段（例如：当前季度是 2，所以我想选择 2020 年第 1 季度和 2019 年第 4 季度的所有字段）

这是我的查询：

SELECT e1.user_id, 
e1.quarter AS last_quarter, 
e1.year AS last_year, 
e1.content AS content_last_quarter, 
e2.quarter AS quarter, 
e2.year AS year, 
e2.content AS content_quarter 
FROM evaluations AS e1 JOIN evaluations AS e2 ON e2.user_id = e1.user_id
WHERE (e1.year = 2019) 
    AND (e1.quarter = 4) 
    AND (e2.year = 2020)) 
    AND (e2.quarter = 1) 
    AND e1.deleted_at IS NULL
    AND e2.deleted_at IS NULL

但如果（2020 年第 1 季度）的记录存在，（2019 年第 4 季度）的记录为空，反之亦然，则无结果。我想选择是否存在或两者都存在。谁能帮我？

对不起，我的英语水平不好。

谢谢！

Answer 1

使用条件聚合：

SELECT e.user_id, 
       MAX(e.quarter) FILTER (WHERE year = 2019) as last_quarter, 
       MAX(e.quarter) FILTER (WHERE year = 2019) as last_year, 
       MAX(e.content) FILTER (WHERE year = 2019) as last_content, 
       MAX(e.quarter) FILTER (WHERE year = 2020) as quarter, 
       MAX(e.quarter) FILTER (WHERE year = 2020) as year, 
       MAX(e.content) FILTER (WHERE year = 2020) as content
FROM evaluations e
WHERE ((e.year = 2019 AND e.quarter = 4) OR
       (e.year = 2020 AND e.quarter = 1) 
      ) AND
      e.deleted_at IS NULL
GROUP BY e.user_id;