SQL表合併

Question

使用SQL Server 2008，我會盡我所能來描述我想要做什麼。

比方說，我有一個看起來像這樣的表答：

表A

VarName | ValueA | ValueB 
----------------------------- 
var1  | 0.12 | 0.34 
var2  | 1.456 | 5.31 
var3  | 43  | 10 

而且，看起來像這樣的表B：

表B

VarName | ValueC | ValueD 
----------------------------- 
var1  | 0.03 | 0.04 
var2  | 2.01 | 2.87 
newvar | 55  | 50 

我想要做的就是把這些表結合起來，這樣最終結果就像這張表C.

表C

VarName | ValueA | ValueB | ValueC | ValueD 
--------------------------------------------------- 
var1  | 0.12 | 0.34 | 0.03 | 0.04 
var2  | 1.456 | 5.31 | 2.01 | 2.87 
var3  | 43  | 10 | 0  | 0 
newvar | 0  | 0  | 55 | 50 

注意，合併時，共同的行（VAR名）與值是不常見的列和變量在一個表中不存在更新，從其他表有其從另一個表中合併的列設置爲0，例如表B中的newvar和表A中的var3。

此請求是否有意義或需要進一步解釋？

Answer 1

你可以試試：

select VarName, max(ValueA), max(ValueB), max(ValueC), max(ValueD) from (
    select VarName, ValueA, ValueB, 0 as ValueC, 0 as ValueD 
    from TableA 
    union all 
    select VarName, 0, 0, ValueC, ValueD 
    from TableB 
) 
group by VarName 

Answer 2

如何：

SELECT 
    VarName 
    ,MAX(IValueA) AS ValueA 
    ,MAX(ValueB) AS ValueB 
    ,MAX(ValueC) AS ValueC 
    ,MAX(ValueD) AS ValueD 
FROM ( 
SELECT 
    VarName 
    ,ValueA 
    ,ValueB 
    ,0 AS ValueC 
    ,0 AS ValueD 
FROM A 
UNION ALL 
SELECT 
    VarName 
    ,0 AS ValueA 
    ,0 AS ValueB 
    ,ValueC 
    ,ValueD 
FROM B 
) a 
GROUP BY VarName