我想知道是否有另一種方式來寫這個查詢

Question

SELECT orderyear, numcusts 
FROM (SELECT orderyear, COUNT (DISTINCT custid) AS numcustd 
     FROM (SELECT YEAR()orderdate) AS orderyear, custid 
FROM sales,Orders) AS D1 
GROUP BY orderyear) AS D2 

WHERE numcusts > 70; 

Answer 1

SELECT orderyear, 
      COUNT (DISTINCT custid) AS numcustd 
     FROM (SELECT YEAR(orderdate) AS orderyear, 
        custid 
       FROM sales, 
        Orders) AS D1 
    GROUP BY orderyear 
    HAVING COUNT (DISTINCT custid) > 70; 

OR

SELECT YEAR(orderdate) AS orderyear, 
      COUNT(DISTINCT custid) AS numcustd 
     FROM sales, 
      orders 
    GROUP BY YEAR(orderdate) 
    HAVING COUNT(DISTINCT custid) > 70; 

Answer 2

• 沒有在查詢一個錯字：YEAR()orderdate)應該YEAR (orderdate)。
• 您正在使用過時的語法進行交叉連接：FROM sales,Orders。改爲使用FROM sales CROSS JOIN Orders。但是，你真的想要交叉連接嗎？爲什麼要把所有的銷售和所有的訂單結合起來更可能的是你實際上想要一個內部聯接（FROM sales INNER JOIN Orders ON ...）或者甚至是兩個表的聯合。
• 您可以合併兩個最內層的查詢。
• 您可以通過直接應用HAVING COUNT (DISTINCT custid) > 70來擺脫最外面的查詢。

Answer 3

試試這個：

SELECT D1.orderyear, D1.numcustd 
FROM (
     SELECT YEAR(orderyear) as orderyear, COUNT (DISTINCT custid) AS numcustd 
     FROM sales,Orders 
     GROUP BY orderyear 
          ) AS D1 
WHERE numcusts > 70;