如何解決這個特定的查詢？

Question

table1   table2 

col1 date  col1 date 
a d1  e  d4 
b d2  f  d5 
c d3  a  d6 

我想這有4項order by date但if any entries of column 1 replicate it remove this duplication also. 新表想，如果我的日期順序d1>d6>d2>d3>d5>d4那麼結果應該是：

col1 date 
a  d1 
b  d2 
c  d3 
e  d5 

而且我也想知道哪些數據是從tabl1未來或表2。

Answer 1

試試這個：

select 
top 4 --you only need 4 of them? 
col1, min(date) [date] from 
(
select col1, date from table1 
union 
select col1, date from table2 
) t 
group by col1 
order by col1 

Answer 2

select 
     col1, 
     min(date) date 
    from 
     (select col1, date 
      from table1 
     union all 
     select col1, date 
      from table2) 
    limit 4 
    group by 
     1 
    order by 
     2 

從數據樣本中，我認爲你想要5個條目..你錯過了你的數據元素「f」。