訪問/ SQL查詢JOIN創建的表

Question

我已經以下查詢：

SELECT t1.Material, t1.Amount, t2.amtLast, t3.amtLast 
FROM FAUF t1 
LEFT JOIN 
    (SELECT FAUF.Material AS mat, FAUF.Amount AS amtLast 
    FROM FAUF 
    WHERE (year=2014)) t2 
    ON (t1.Material = t2.mat) 
LEFT JOIN 
    (SELECT FAUF.Material AS mat, FAUF.Amount AS amtLast 
    FROM FAUF 
    WHERE (year=2013)) t3 
    ON (t1.Material = t3.mat) 
WHERE (t1.year=2015); 

MS訪問被給我一個誤差，即一個表達中缺少（t1.Material = t2.mat）。如果我排除最後一次JOIN查詢的工作原理，我錯過了什麼？

Answer 1

MS Access需要額外的連接括號。試試這個：

SELECT t1.Material, t1.Amount, t2.amtLast, t3.amtLast 
FROM (FAUF t1 LEFT JOIN 
     (SELECT FAUF.Material AS mat, FAUF.Amount AS amtLast 
     FROM FAUF 
     WHERE (year=2014) 
    ) t2 
    ) 
    ON (t1.Material = t2.mat) LEFT JOIN 
    (SELECT FAUF.Material AS mat, FAUF.Amount AS amtLast 
     FROM FAUF 
     WHERE (year=2013) 
    ) t3 
    ON (t1.Material = t3.mat) 
WHERE (t1.year = 2015); 

但是，您可以使用條件聚集，這比join方法更簡單的做到這一點：

select f.Material, 
     sum(iif(f.year = 2015, amount, 0)) as amt_2015, 
     sum(iif(f.year = 2014, amount, 0)) as amt_2014, 
     sum(iif(f.year = 2013, amount, 0)) as amt_2013 
from fauf f 
group by f.Material;