僅返回MySQL中列的最高值

任何人都可以解釋如何解決這個問題嗎？僅返回MySQL中列的最高值

SELECT book_id, title, count(DISTINCT order_id) 
FROM a_bkinfo.books 
JOIN a_bkinfo.book_topics USING (book_id) 
JOIN a_bkorders.order_details USING (book_id) 
WHERE topic_id IN ("FCT", "POE") 
GROUP BY book_id; 


1077 Programming for Poets 2 
1103 Selected Poems 34 
1133 Leaves of Grass 4 
1304 Stories of Discoveries 6 
1306 Myths of SQL 3 
1602 Goblin Market and Other Poems 4

我只想要返回右側最高值的行（即「Selected Poems」）。我將如何去完成這件事？

來源

2015-03-19 Blobert

什麼是努力實現？ – 2015-03-19 01:45:10

我試圖讓'max（count（DISTINCT order_id））'返回一個數字而不是一個錯誤。 – Blobert 2015-03-19 02:09:36

完成此操作的典型方法是按降序對計數表達式進行排序，然後將結果限制爲一行。如果你需要關係，那麼你可能不得不採取其他方法之一。 – shawnt00 2015-03-19 03:10:07

select max(order_count) from (
    SELECT count(DISTINCT order_id) as order_count 
    FROM a_bkinfo.books 
    JOIN a_bkinfo.book_topics USING (book_id) 
    JOIN a_bkorders.order_details USING (book_id) 
    WHERE topic_id IN ("FCT", "POE") 
    GROUP BY book_id 
) T

這是一個標量的結果，所以你應該能夠添加到您的原始查詢的選擇列表，如果你想看到它附加到每一行：

select ..., (
    select max(order_count) from (
     SELECT count(DISTINCT order_id) as order_count 
     FROM a_bkinfo.books 
     JOIN a_bkinfo.book_topics USING (book_id) 
     JOIN a_bkorders.order_details USING (book_id) 
     WHERE topic_id IN ("FCT", "POE") 
     GROUP BY book_id 
    ) as max_order_count 
from ...

，或者您可以使用交叉加入

select ... 
from ... 
    JOIN a_bkorders.order_details USING (book_id), 
    (
     select max(order_count) from (
      SELECT count(DISTINCT order_id) as order_count 
      FROM a_bkinfo.books 
      JOIN a_bkinfo.book_topics USING (book_id) 
      JOIN a_bkorders.order_details USING (book_id) 
      WHERE topic_id IN ("FCT", "POE") 
      GROUP BY book_id 
     ) T 
    ) T2 
where ...

不確定哪個是MySQL的更好選擇。

這最後一個選項與最大值的行（S）將返回：

SELECT book_id, title, count(DISTINCT order_id) 
FROM a_bkinfo.books 
JOIN a_bkinfo.book_topics USING (book_id) 
JOIN a_bkorders.order_details USING (book_id) 
WHERE topic_id IN ("FCT", "POE") 
GROUP BY book_id 
HAVING count(DISTINCT order_id) = (
    select max(order_count) from (
     SELECT count(DISTINCT order_id) as order_count 
     FROM a_bkinfo.books 
     JOIN a_bkinfo.book_topics USING (book_id) 
     JOIN a_bkorders.order_details USING (book_id) 
     WHERE topic_id IN ("FCT", "POE") 
     GROUP BY book_id 
    ) 
)

來源

2015-03-19 02:39:44 shawnt00

謝謝。我會在什麼地方把它放在原來的區塊中，這樣它會返回右邊那個數字最高的那一行？ HAVING count（DISTINCT order_id）= select max（order_count）from（ SELECT count（DISTINCT order_id）as order_count FROM a_bkinfo.books JOIN a_bkinfo.book_topics USING（book_id） JOIN a_bkorders.order_details USING（book_id） WHERE topic_id IN（「FCT」，「POE」） GROUP BY book_id ）T'但它返回一個錯誤。 – Blobert 2015-03-19 02:58:24

也許我仍然錯誤地想要什麼。如果你想使用'having'，那麼把整個查詢包裝在另一組圓括號中，並從最後的T中包裝。我不確定它會在MySQL上工作，但它應該可以在其他平臺上工作。 – shawnt00 2015-03-19 03:08:15

我只想返回具有最高命令（並且只有那本書）的書 - 具有最高輸出的書：'（count（DISTINCT order_id）'。是否有用MySQL來做這件事？'HAVING count（ DISTINCT order_id）= max（count（DISTINCT order_id）'由於某種原因返回一個錯誤，但是'HAVING count（DISTINCT order_id）= 34'似乎有效，所以我不確定錯在哪裏。 – Blobert 2015-03-19 03:13:19

僅返回MySQL中列的最高值

回答

相關問題