mysql - 使用 CASE 时指定 SUM 列

Question

我基本上是在尝试总结特定列的值。现在我的查询如下所示:

SELECT
DATE(paid_at) AS day,
(SELECT sum(shipping_costs) from orders where shipping_method = 'mondial_relais' and DATE(paid_at) = day) as mr_revenue_real
FROM orders
WHERE MONTH(paid_at) = 10
AND YEAR(paid_at) = 2011
GROUP BY day;

我想替换 mr_revenue_real 的子查询以提高性能，但我不知道该怎么做。这就是我的想法: sum(case when hipping_method = 'mondial_relais' and DATE(paid_at) = day then 1 end) as mr_revenue_real但这不起作用，因为我没有在任何需要运费总和的地方指定.

有什么想法吗？

Answer 1

sum(case when  shipping_method='mondial_relais' then shipping_costs else 0 end)

完整查询:

SELECT
 DATE(paid_at) AS day,
 sum(case when  shipping_method='mondial_relais' then shipping_costs else 0 end)
FROM orders
WHERE MONTH(paid_at) = 10 AND YEAR(paid_at) = 2011
GROUP BY day;