從表中爲每個主鍵獲取頂部數據

Question

我有一系列外鍵，每個鍵構成表中的多行。我怎樣才能只提取符合指定條件的頂行？

我有表這樣

ID NAME  DATE 
---------------------- 
1  abc  5/10/15 
1  abc  6/11/15 
2  pqr  7/11/15 
2  pqr  8/10/15 
3  xyz  9/12/15 

我需要輸出是這樣

其中所述病症是日期> 15年5月11日和ID中（1,2）

ID NAME DATE 
----------------- 
1 abc 6/11/15 
2 pqr 7/11/15 

Answer 1

你可以用row_number()來做你想做的事。我不確定你想要什麼。我最好的猜測越來越有符合條件的最小日期行：

select t.* 
from (select t.*, 
      row_number() over (partition by id order by date) as seqnum 
     from t 
     where date > '2015-11-05' and id in (1, 2) 
    ) t 
where seqnum = 1; 

Answer 2

使用NOT EXISTS只要返回行，因爲沒有其他行具有相同的名稱和一個較早的日期：

select t1.* 
from tablename t1 
where not exists (select * from tablename t2 
        where t2.name = t1.name 
        and t2.date < t1.date 
        and t2.date > '5/11/15' and t2.ID in (1,2)) 
    and t1.date > '5/11/15' and t1.ID in (1,2) 

JOIN替代，也許更能MySQL的答案：

select t1.* 
from tablename t1 
    join (select name, min(date) from tablename 
      where date > '5/11/15' and t2.ID in (1,2) 
      group by name) as t2 
     on t1.name = t2.name and t1.date = t2.date 
where t1.date > '5/11/15' and t1.ID in (1,2) 

核心SQL-99。