SQL Server：UPDATE語句，其中MAX查詢

Question

我正在SQL Server 2008 R2中進行數據遷移。我是SQL-Server noob，但我很瞭解Ingres和MySql。

我需要將兩個新字段的「默認值」設置爲另一個表中的「當前值」。這是我第一次天真的嘗試（我將如何在Ingres做到這一點）。

update rk_risk 
set  n_target_probability_ID = a.n_probability_ID 
     , n_target_consequence_ID = a.n_consequence_ID 
from rk_assess a 
WHERE a.n_assess_id = (
    SELECT MAX(n_assess_id) 
    FROM rk_assess a2 
    WHERE a2.n_risk_id = a.n_risk_id 
); 

上面的查詢執行沒有在續集中的錯誤，不過這臺ALL的n_target_probability_ID的& n_target_consequence_ID的到相同的值 ...的奪標最後一次評估（如並列爲「最後評估這個風險「）。

的rk_assess表中包含的評估記錄的完整歷史rk_risk秒，我的使命是「默認」的新目標概率&後果的風險表中的值列從「當前」（即最後一個）評估記錄。 rk_assess.n_assess_id列是一個自動遞增的標識符（一次設置不變），所以max-id應該是最後輸入的記錄。

我已經有一個搜索，無論是在谷歌和SO，並嘗試了幾個不同版本的查詢，但我仍然堅持。這裏有一些其他的史詩般的失敗，並帶有參考。

update rk_risk 
set  n_target_probability_ID = (select a.n_probability_ID from rk_assess a where a.n_assess_id = (select max(n_assess_id) from rk_assess a2 where a2.n_risk_id = a.n_risk_id) as ca) 
     , n_target_consequence_ID = (select a.n_consequence_ID from rk_assess a where a.n_assess_id = (select max(n_assess_id) from rk_assess a2 where a2.n_risk_id = a.n_risk_id) as ca) 
; 

http://stackoverflow.com/questions/6256844/sql-server-update-from-select 

update r 
set  r.n_target_probability_ID = ca.n_probability_ID 
     , r.n_target_consequence_ID = ca.n_consequence_ID 
from rk_risk r 
join rk_assess a 
on  a.n_risk_id = r.n_risk_id 

select r.n_risk_id 
      , r.n_target_probability_ID, r.n_target_consequence_ID 
      , ca.n_probability_ID, ca.n_consequence_ID 
from rk_risk r 
join rk_assess a 
on  a.n_risk_id = r.n_risk_id 

http://stackoverflow.com/questions/4024489/sql-server-max-statement-returns-multiple-results 

UPDATE rk_risk 
SET  n_target_probability_ID = ca.n_probability_ID 
     , n_target_consequence_ID = ca.n_consequence_ID 
FROM (rk_assess a 
INNER JOIN (
     SELECT MAX(a2.n_assess_id) 
     FROM rk_assess a2 
     WHERE a2.n_risk_id = a.n_risk_id 
) ca -- current assessment 

任何指針將不勝感激。提前謝謝大家，甚至可以閱讀這些。

乾杯。基思。

Answer 1

如何：

update rk_risk 
set  n_target_probability_ID = a.n_probability_ID 
     , n_target_consequence_ID = a.n_consequence_ID 
from rk_assess a 
JOIN (
    SELECT n_risk_id, MAX(n_assess_id) max_n_assess_id 
    FROM rk_assess 
    GROUP BY n_risk_id 
    ) b 
ON a.n_risk_id = b.n_risk_id AND a.n_assess_id = b.max_n_assess_id 
WHERE a.n_risk_id = rk_risk.n_risk_id 

Answer 2

我所以只是今天發現了這個來自另外一個問題。 UPDATE-FROM構造不是標準SQL，MySQL的非標準版本與Postgres的非標準版本不同。從這裏的問題看來，SQL Server遵循Postgres。

Jerad在他的編輯中指出，問題是在被更新的表和子查詢中的表之間沒有關聯。 MySQL似乎在這裏創建了一些隱式聯接（在另一個SO例子中的列名稱上，它是通過將同一個表的兩個副本視爲相同的，而不是單獨的）。

我不知道，如果SQL Server允許在子查詢窗口，但如果這樣做，我想你想

UPDATE rk_risk 
set  n_target_probability_ID = a.n_probability_ID 
     , n_target_consequence_ID = a.n_consequence_ID 
from 
    (SELECT * FROM 
    (SELECT n_risk_id, n_probability_ID, n_consequence_ID, 
       row_number() OVER (PARTITION BY n_risk_id ORDER BY n_assess_ID DESC) AS rn 
     FROM rk_assess) 
    WHERE rn = 1) AS a 
WHERE a.n_risk_id=rk_risk.n_risk_id; 

Answer 3

如果你使用SQL 2005或更高版本，您可以除了Jerad的答案使用ROW_NUMBER函數

With b 
(
     SELECT n_risk_id, 
       n_assess_id, 
       n_probability_ID, 
       n_consequence_ID, 
       row_number() over (partition by n_risk_id order by n_assess_id desc) row 
     FROM rk_assess 
) 
update rk_risk 
set  n_target_probability_ID = b.n_probability_ID 
     , n_target_consequence_ID = b.n_consequence_ID 
from b 
WHERE a.n_risk_id = rk_risk.n_assess_id 
     and row =1 

或者CROSS JOIN

update rk_risk 
set  n_target_probability_ID = b.n_probability_ID 
     , n_target_consequence_ID = b.n_consequence_ID 
from rh_risk r 
     CROSS JOIN 
     (
     SELECT TOP 1 
       n_risk_id, 
       n_assess_id, 
       n_probability_ID, 
       n_consequence_ID 
     FROM rk_assess 
     order by n_assess_id desc 
     WHERE a.n_risk_id = r.n_assess_id) b 

Answer 4

我想這一點，看起來是幹活g：

update rk_risk 
set  n_target_probability_ID = a.n_probability_ID, 
     n_target_consequence_ID = a.n_consequence_ID 
from rk_assess a, rk_risk r 
WHERE a.n_risk_id = r.n_risk_id 
and a.n_assess_id in (select MAX(n_assess_id) from rk_assess group by n_risk_id)