連接表，其中> 1行中的子表

Question

我有幾個表返回單列，books, bookcategories, categories

bookcategories是連接表，讓許多人books和categories之間一對多的關係。

我希望能夠在書上運行類別搜索，以便即使書中有很多類別時，搜索也會返回每行一行。

書籍

ID | Title 
1 | Once upon... 
2 | How many... 
3 | How much... 

分類

ID | Category 
1 | x 
2 | y 
3 | z 

BookCategories

BookId | CategoryId 
    1 |  1 
    1 |  2 
    2 |  2 
    2 |  3 
    2 |  1 
    3 |  1 

我以爲我可以逃脫這個：

SELECT b.Id, 
    b.Title, 
FROM (books b 
    INNER JOIN bookcategories bc ON b.ID= bc.BookId 
    ) 
WHERE (bc.categoryId =1 AND bc.categoryId=2) 
GROUP BY b.Id, b.Title 

但是，只要我添加AND，查詢就不會返回任何行。但是，這是我需要申請的標準 - 我只想返回書籍行，其中書籍同時具有上述類別1和2（即，不是類別1或類別2）

不禁讓我以爲我失蹤一些基本的東西。誰能幫忙？

我需要改變表格的結構還是有辦法實現我所需要的。

永

Answer 1

這應該歸還圖書有兩個類別之一，之二：

select b.Id 
,  b.Title 
from books b 
join bookcategories bc 
on  bc.BookId = b.Id 
group by 
     b.Id 
,  b.Title 
having sum(case when bc.categoryId = 1 then 1 end) > 0 
     and sum(case when bc.categoryId = 2 then 1 end) > 0 

另外，也可以使用雙exists條款：

select b.Id 
,  b.Title 
from books b 
where exists 
     (
     select * 
     from bookcategories bc 
     where bc.BookId = b.Id 
       and bc.CategoryId = 1 
     ) 
     and exists 
     (
     select * 
     from bookcategories bc 
     where bc.BookId = b.Id 
       and bc.CategoryId = 2 
     ) 

Answer 2

嘗試增加select distinct和改變and改爲or。

SELECT  DISTINCT b.Id, b.Title 
FROM  books b 
INNER JOIN bookcategories bc ON b.ID= bc.BookId 
WHERE  (bc.categoryId=1 OR bc.categoryId=2) 
ORDER BY b.ID 

distinct關鍵字不會返回重複的行;所以你現在可以使用categoryID = 1 OR categoryID = 2。

Answer 3

另一種選擇（至少根據我想你想要）：

SELECT ID, Title 
FROM 
(
    SELECT b.ID, b.Title, c = COUNT(bc.BookID) 
    FROM dbo.Books AS b 
    INNER JOIN dbo.BookCategories AS bc 
    ON b.ID = bc.BOokID 
    AND bc.CategoryID IN (1,2) 
    GROUP BY b.ID, b.Title 
) AS x 
WHERE c >= 2; -- in case there is no unique constraint on BookCategories 

雖然這應該也行：

SELECT b.ID, b.Title 
    FROM dbo.Books AS b 
    INNER JOIN dbo.BookCategories AS bc 
    ON b.ID = bc.BOokID 
    AND bc.CategoryID IN (1,2) 
GROUP BY b.ID, b.Title 
HAVING COUNT(*) >= 2;