如何在 SQL 命令行中按月汇总值？

Question

我想总结一个变量，它是来自 2 个不同表的 2 个变量的总和。

SELECT EXTRACT(MONTH FROM Service.EDate) AS MONTH, 
       SUM(Insurance.Price+Service.Charge) AS PROFIT
FROM 
Service INNER JOIN 
Insurance ON Service.Code=Insurance.Code
WHERE EXTRACT(YEAR FROM Service.EDate)=2018
GROUP BY Service.EDate
ORDER BY Service.EDate;

预计答案是 MONTH 有 1 个值（1,2,3,4,5 等和利润总结）但我得到 MONTH 像利润（[1,105],[1,405],[1,320 ],[2,410],[2,110] 等具有 [MONTH,PROFIT])

Answer 1

您似乎想要GROUP BY中的MONTH ：

SELECT EXTRACT(MONTH FROM s.EDate) AS MONTH, 
       SUM(i.Price + s.Charge) AS PROFIT
FROM Service s INNER JOIN 
     Insurance i
     ON s.Code = i.Code
WHERE EXTRACT(YEAR FROM s.EDate) = 2018
GROUP BY EXTRACT(MONTH FROM s.EDate)
ORDER BY EXTRACT(MONTH FROM s.EDate);

请注意，我添加了表别名，因此查询更易于编写和阅读。

我建议对WHERE子句使用日期比较而不是EXTRACT() ：

WHERE s.EDate >= DATE '2018-01-01' AND
      s.EDate < DATE '2019-01-01'

这有助于优化器，尤其是可以使用索引。