在同一个查询中计算和求和？

Question

所以我有一个可以提供总和成本的查询：

SELECT ROUND(SUM(cost), 2) AS 'Sum of Cost', 
MONTH(startDateTime) AS Month,
MONTHNAME(STR_TO_DATE(MONTH(startDateTime), '%m')) month_name
FROM Event
GROUP BY Month;

我想要添加到此查询中的另一件事是事件发生在每个月的次数，因为它们是几个月在同一天发生事件，从而影响事件的总和。

Answer 1

首先按照逻辑顺序

更新您的论坛

SELECT ROUND(SUM(cost), 2) AS 'Sum of Cost', MONTH(startDateTime) AS Month
FROM Event
GROUP BY  MONTH(startDateTime);

Answer 2

由于您按月分组，您可以在同一句话中同时使用SUM和COUNT。

SELECT ROUND(SUM(cost), 2) AS 'Sum of Cost', 
       MONTH(startDateTime) AS Month,
       MONTHNAME(STR_TO_DATE(MONTH(startDateTime), '%m')) month_name,
       COUNT(*) as NumEvents
FROM Event
GROUP BY MONTH(startDateTime);