Mysql：如何连接两个表并查找每个公司最近一年的收入

问题描述

这是两个包含数据的表，如何将这两个表连接起来并查找每个表的收入 公司的最新可用年份。如何编写SQL查询以获取预期结果？

  Table ‘Companies’:

    Id | companyCode| companyName
    1 | comp1      | Tata Motors
    2 | comp2      | Reliance
    3 | comp3      | Infosys
    4 | comp4      | HDFCBANK

 Table ‘FinancialDatas’

   Id | companyCode| year | revenue
   12 | comp1      | 2019 | 12500
   13 | comp1      | 2020 | 13250
   14 | comp2      | 2018 | 45000
   15 | comp2      | 2019 | 55000
   16 | comp3      | 2019 | 9500
   17 | comp3      | 2020 | 7500
   18 | comp4      | 2017 | 11000
   19 | comp4      | 2018 | 13500

Extexted OutPut Below:

  companyName | year | revenue
  Tata Motors |2020  |13250
  Reliance    |2019  |55000
  Infosys     |2020  |7500
  HDFCBANK    |2018  |13500 

解决方法

您可以使用row_number()

select * from
(
select companyName,year,revenue,row_number() over(partition by companyName order by year desc) as rn
from companies c join FinancialDatas f on c.companycode=f.companycode
)A where rn=1