不是工作

Question

一個SQL的例子，我在練習14寫了這個代碼

select maker.product , product.type 
from product 
join laptop on laptop.model=product.model 
join pc on pc.model=product.model 
join printer on printer.model=product.model 
WHERE (product.type= 'pc' AND 
(NOT EXISTS (SELECT maker 
FROM Product 
WHERE product.type = 'laptop' 
))and (NOT EXISTS (SELECT maker 
FROM Product 
WHERE product.type = 'printer' 
)) 
or 
product.type= 'laptop' AND 
(NOT EXISTS (SELECT maker 
FROM Product 
WHERE product.type= 'pc' 
))and (NOT EXISTS (SELECT maker 
FROM Product 
WHERE product.type= 'printer' 
)) 
or 
type = 'printer' AND 
(NOT EXISTS (SELECT maker 
FROM Product 
WHERE product.type= 'laptop' 
))and (NOT EXISTS (SELECT maker 
FROM Product 
WHERE product.type= 'pc' 
))) 
group by product.maker 
having count(product.model) > 1 

在這個網站sql-ex.ru，但沒有奏效。 問題是： 對於產品表，得到的結果與列的表的形式設置：製造商，PC，筆記本電腦和printer.For每個製造商，該表必須包含「是」如果製造商具有相應類型的產品否則爲「否」。在第一種情況下（是），在括號（無空格）中指定相應類型（即在PC，筆記本電腦和打印機表格中）的可用不同型號的數量。

而且它的計劃是

對不起，我不好講英語！ 請幫忙！ 謝謝。

Answer 1

這是你的代碼的可讀性更強的版本（除非我犯了一個錯誤）：

select maker.product , product.type 
from product 
join laptop on laptop.model=product.model 
join pc on pc.model=product.model 
join printer on printer.model=product.model 
WHERE (
    product.type= 'pc' AND 
    (NOT EXISTS (SELECT maker FROM Product WHERE product.type = 'laptop')) and 
    (NOT EXISTS (SELECT maker FROM Product WHERE product.type = 'printer')) 
    or 
    product.type= 'laptop' AND 
    (NOT EXISTS (SELECT maker FROM Product WHERE product.type= 'pc')) and 
    (NOT EXISTS (SELECT maker FROM Product WHERE product.type= 'printer')) 
    or 
    type = 'printer' AND 
    (NOT EXISTS (SELECT maker FROM Product WHERE product.type= 'laptop')) and 
    (NOT EXISTS (SELECT maker FROM Product WHERE product.type= 'pc')) 
) 
group by product.maker 
having count(product.model) > 1 

基本上，它看起來像你需要的每一個之間做括號中的OR的。