MySQL 数据透视查询

Question

我曾经有一个查询

SELECT ps_target_ecpm, ps_actual_ecpm
FROM publisher_stats
JOIN domain ON domain.dmn_id = ps_dmn_id
LEFT JOIN langue ON langue.lng_id = domain.default_lng_id
WHERE MONTH(ps_month) = 05 

我需要的结果应该是这样的

may_target_ecmp、may_actual_ecpm、april_target_ecpm、 april_actual_ecpm、march_target_ecpm、march_actual_ecpm。

4 月 MONTH(ps_month) = 04 和 3 月 MONTH(ps_month) = 03 分别。

经过一番询问，我最终得到了一个看起来像这样的查询

SELECT
(CASE WHEN MONTH(ps_month) = 4 THEN ps_target_ecpm ELSE 0 END) AS april_target_ecpm, 
(CASE WHEN MONTH(ps_month) = 4 THEN ps_actual_ecpm ELSE 0 END) AS april_actual_ecpm,
(CASE WHEN MONTH(ps_month) = 3 THEN ps_target_ecpm ELSE 0 END) AS march_target_ecpm, 
(CASE WHEN MONTH(ps_month) = 3 THEN ps_actual_ecpm ELSE 0 END) AS march_actual_ecpm 
FROM publisher_stats
JOIN domain ON domain.dmn_id = ps_dmn_id
LEFT JOIN langue ON langue.lng_id = domain.default_lng_id

我得到的结果不是我所需要的。 示例响应是：

0           0       0.48    0.27
0.48        0.47    0       0

虽然我需要它在一行中

0.48    0.47    0.48    0.27

能否请您帮我弄清楚如何使这个查询达到预期的效果。 提前致谢

附：这个问题从这个问题一路而来——mysql pivoting - how can I fetch data from the same table into different columns?

Answer 1

只需使用聚合函数，例如 MAX 就可以正常工作，但如果您需要获取每个月的总数，如果每个月有多个 ps_target_ecpm 条目，您可能需要使用 SUM .像这样：

SELECT
  MAX(CASE WHEN MONTH(ps_month) = 4 THEN ps_target_ecpm ELSE 0 END) AS april_target_ecpm, 
  MAX(CASE WHEN MONTH(ps_month) = 4 THEN ps_actual_ecpm ELSE 0 END) AS april_actual_ecpm,
  MAX(CASE WHEN MONTH(ps_month) = 3 THEN ps_target_ecpm ELSE 0 END) AS march_target_ecpm, 
  MAX(CASE WHEN MONTH(ps_month) = 3 THEN ps_actual_ecpm ELSE 0 END) AS march_actual_ecpm 
FROM publisher_stats
JOIN domain ON domain.dmn_id = ps_dmn_id
LEFT JOIN langue ON langue.lng_id = domain.default_lng_id