如何處理重複在SQL的UNION ALL SELECT語句

Question

舉個例子，如果有：中

SELECT 'A@G.com' AS Email, 2 AS Somenumber, 3 AS Number 
UNION ALL 
SELECT 'A@G.com' AS Email, 2 AS Somenumber, 5 AS Number 
UNION ALL 
SELECT 'z@y.com' AS Email, 1 AS Somenumber, 6 AS Number 

代替：

我想：

Answer 1

SELECT Email, Somenumber, Number 
FROM (
    SELECT *, RowNum = ROW_NUMBER() OVER (PARTITION BY Email ORDER BY Number DESC) 
    FROM (
     VALUES 
      ('A@G.com', 2, 3), 
      ('A@G.com', 2, 5), 
      ('z@y.com', 1, 6) 
    ) t(Email, Somenumber, Number) 
) t 
WHERE RowNum = 1 

輸出 -

Email Somenumber Number 
------- ----------- ----------- 
A@G.com 2   5 
z@y.com 1   6 

Answer 2

它看起來像你在每個電子郵件後一行金正日。你可以這樣做：

; with all_rows as 
     (
     ... your union query here ... 
     ) 
, with numbered_rows as 
     (
     select row_number() over (partition by email order by somenumber) as rn 
     ,  * 
     from all_rows 
     ) 
select email 
,  somenumber 
,  number 
from numbered_rows 
WHERE rn = 1 

Answer 3

通常當我需要解決這樣的問題，我將與以上只是我的腦海Devart解決方案相同的方式 工作，但這裏給出更好的執行計劃的替代解決方案

select Email, max(Somenumber), max(Number) from (
SELECT 'A@G.com' AS Email, 2 AS Somenumber, 3 AS Number 
UNION ALL 
SELECT 'A@G.com' AS Email, 2 AS Somenumber, 5 AS Number 
UNION ALL 
SELECT 'z@y.com' AS Email, 1 AS Somenumber, 6 AS Number 
) A 
group by Email