SQL根据数据按月计算汇总数据

如何解决SQL根据数据按月计算汇总数据

我有一张巨大的桌子，上面有几个月的产品订单历史记录。我想将表格展平，以将列作为日期字段并订购总金额。见下表：

理想的输出是：

我已经尝试过 case 语句

Case when ReportMonth = '2021-07-01' then sum(total) end as '2021-07-01',Case when ReportMonth = '2021-06-01' then sum(total) end as '2021-06-01',Case when ReportMonth = '2021-05-01' then sum(total) end as '2021-05-01',Case when ReportMonth = '2020-05-01' then sum(total) end as '2020-05-01',

但后来我得到了空值和更多记录。

解决方法

考虑通过在 CASE 中运行 SUM 语句来反转嵌套表达式：

SELECT 
     Parent_Org
    --,...other group columns,Category,SUM(CASE WHEN ReportMonth = '2021-07-01' THEN total END) AS '2021-07-01',SUM(CASE WHEN ReportMonth = '2021-06-01' THEN total END) AS '2021-06-01',SUM(CASE WHEN ReportMonth = '2021-05-01' then total END) AS '2021-05-01',SUM(CASE WHEN ReportMonth = '2020-05-01' THEN total END) AS '2020-05-01'
FROM myTable
GROUP BY
     Parent_Org
    --,Category