字段1在字段2上复制，需要根据字段3选择1，并返回字段1和字段2

Question

我有一个包含3个字段的数据列表，ISIN，CompanyId和EffectiveDate。 ISIN在公司ID和生效日期都被复制。

实施例的数据：

ISIN   CompanyId EffectiveDate 
AED001410045 58105545  2012-02-09 
AEDFXA1G39P8 132844116 2016-04-22 
AEDFXA1G39P8 132844116 2017-09-21 
ARDEUT110020 249603  2012-02-09 
ARDEUT110020 416264458 2017-03-22 

使用

SELECT ISIN, CompanyId, MAX(EffectiveDate) 
FROM [MappingData].[dbo].[ESGMappingISIN] 
GROUP BY ISIN,CompanyId 

我可以删除关于ISIN和CompanyId重复项以返回

ISIN   CompanyId EffectiveDate 
AED001410045 58105545  2012-02-09 
AEDFXA1G39P8 132844116 2017-09-21 
ARDEUT110020 249603  2012-02-09 
ARDEUT110020 416264458 2017-03-22 

的最后一步，我需要的是：

A) Return ISIN and CompanyId where ISIN is distinct 
B) If 1 ISIN has 2 CompanyIds, return the line with the later effective date. 

理想输出

ISIN   CompanyId EffectiveDate 
AED001410045 58105545  2012-02-09 
AEDFXA1G39P8 132844116 2017-09-21 
ARDEUT110020 416264458 2017-03-22 

Answer 1

您可以使用row_number()：

SELECT * 
FROM (SELECT ISIN, CompanyId, MAX(EffectiveDate) as maxed, 
      ROW_NUMBER() OVER (PARTITION BY ISIN ORDER BY MAX(Effectivedate) DESC) as seqnum 
     FROM [MappingData].[dbo].[ESGMappingISIN] 
     GROUP BY ISIN, CompanyId 
    ) m 
WHERE seqnum = 1; 

Answer 2

您可以使用这样的子查询：

SELECT 
    B.ISIN, 
    B.CompanyID, 
    B.EffectiveDate 
FROM 
    (
     SELECT 
     ISIN, 
     CompanyId, 
     MAX(EffectiveDate) AS EffectiveDate 
     FROM 
     ESGMappingISIN 
     GROUP BY 
     ISIN, 
     CompanyId 
    ) 
    AS B 
    JOIN 
     (
     SELECT 
      ISIN, 
      MAX(EffectiveDate) AS EffectiveDate 
     FROM 
      ESGMappingISIN 
     GROUP BY ISIN 
    ) AS A 
     ON B.ISIN = A.ISIN 
     AND B.EffectiveDate = A.EffectiveDate