SQL Join 按表分组答案

【问题标题】：SQL Join with a group by tableSQL Join 按表分组
【发布时间】：2021-07-11 00:35:14
【问题描述】：

您好，我需要您的帮助：

表 A 每次员工联系公司时都会有一行

ID	Name	Company	Industry	Segment	Date	Manager
1	John	XYZ	Services	Corp	2021-03-01	Peter
2	John	ABC	Manufacturing	Corp	2021-03-01	Peter
3	Rachel	DEF	Services	MidMarket	2021-03-05	Maria

表 B 的每月目标是每个行业和细分的“覆盖率”或“计数 ID”：

Industry	Segment	Month and Year	Target Companies	Target Count ID
Manufacturing	Corp	2021-03-01	100	15
Manufacturing	MidMarket	2021-03-01	120	20
Services	Corp	2021-03-01	80	10
Services	MidMarket	2021-03-01	95	35

现在我正在加入这两个表，以按月查看目标与实际情况，如下所示：

**Temporary Table**
Select
'Industry', 
'Segment', 
LAST_DAY(('Date') - INTERVAL 1 MONTH) + INTERVAL 1 DAY AS 'Month and Year',
Count ('ID') as 'a.Count_ID',
Count (Distinct ('Company') as 'a.Count_Company'
From Table A
Group by
1,2

Select
'a.Industry', 
'a.Segment', 
'a.Month and Year',
'a.Count_ID',
'a.Count_Company',
'b.Target Companies',
'b.Target Count ID'
From temporary table as a Left Join Table B as b
ON 'a.Industry' = 'b.Industry'
AND a.Segment = 'b.Segment'
AND a.Month and Year' = 'b.Month and Year'

现在我还需要在输出中添加经理和员工姓名，但目标没有按员工和经理拆分。有没有办法在没有 group by 的情况下加入这 2 个表？

【问题讨论】：

编辑您的问题并显示您想要的结果。
默认情况下，（几乎）MySQL 中引号中的任何内容都是字符串。

标签： mysql sql join group-by

【解决方案1】：

加入前聚合。因为可以有多个员工和经理，我建议使用group_concat()：

select b.*, a.num_companies, a.num_contacts, a.names, a.managers
from b join
     (select date + (1 - day(date)) day as year_month,
             industry, segment,
             count(distinct company) as num_companies,
             count(*) as num_contacts,
             group_concat(distinct name) as names,
             group_concat(distinct manager) as managers
      from a
      group by year_month, industry, segment
     ) a
     on a.industry = b.industry and a.segment = b.segment and
        a.year_month = b.year_month

【讨论】：