在select语句中获取每个组的最近条目

Question

我有3个表来加入以获取table1.code，table1.series，table2.entry_date，table3.title1 并且我试图获取最近的非null table1.title1按table1.code和table1.series分组。

select table1.code, table1.series, max(table2.entry_date), table3.Title1 
       from table3 INNER JOIN table2 ON table3.ID = table2.ID 
       INNER JOIN table1 ON table2.source_code = table1.code 
       where table3.Title1 is not NULL 
       group by table1.code, table1.series, table3.Title1 

似乎给了我一个非null的title1而不是最近的所有条目。我应该如何构建查询来挑选最新版本的Title1代码&系列？

Answer 1

试试这个：

select table1.code, table1.series, max(table2.entry_date), max(table3.Title1) as Title1 
from table3 
INNER JOIN table2 ON table3.ID = table2.ID 
INNER JOIN table1 ON table2.source_code = table1.code 
where table3.Title1 is not NULL 
And Table2.entry_Date = (Select Max(sq.entry_Date) 
         From sq.table2 
         Where sq.id = table2.ID) 
group by table1.code, table1.series 

Answer 2

也许这样的事情只能加入在最近的表2项？

SELECT 
    table1.code, 
    table1.series, 
    table2.entry_date, 
    table3.Title1 
FROM 
    table1 
INNER JOIN 
    table2 
ON 
    table2.source_code = table1.code 
AND 
    table2.entry_date = 
(
    SELECT 
     MAX(maxtable2.entry_date) 
    FROM  
     table2 maxtable2 
    WHERE 
     maxtable2.source_code = table2.source_code 
) 
INNER JOIN 
    table3 
ON 
    table3.ID = table2.ID 

Answer 3

;with tlb as 
(
    select table1.code, table1.series, table2.entry_date, table3.Title1, 
    row_number() over(code, series, entry_date order by code, series, entry_date desc) as rn 
    from table3 INNER JOIN table2 ON table3.ID = table2.ID 
    INNER JOIN table1 ON table2.source_code = table1.code 
    where table3.Title1 is not NULL 
) 
select * from tlb where rn = 1 

这可以根据您的指标是非常快的。