儘量減少MySQL查詢的冗餘度

Question

我在嘗試減少MySQL查詢冗餘時遇到了一些麻煩。我目前有它的工作，但它感覺像我有太多的開銷，因爲它使用冗餘子查詢。我所試圖做的是使用DVD租賃數據庫找到其店鋪位置在2005年

這裏已經租出去了更多的DVD每個月爲工作查詢

SELECT b.month, c.store_id, b.maxRentals 
FROM 
    (SELECT a.month, MAX(a.rentalCount) as maxRentals 
    FROM 
     (SELECT MONTH(rental.rental_date) as month, inventory.store_id, count(1) as rentalCount 
     FROM rental 

     INNER JOIN inventory 
     ON rental.inventory_id = inventory.inventory_id 

     WHERE YEAR(rental.rental_date) = 2005 

     GROUP BY MONTH(rental.rental_date), inventory.store_id 
     ) a 
    GROUP BY a.month 
    ) b 

    INNER JOIN 

    (SELECT MONTH(rental.rental_date) as month, inventory.store_id, count(1) as rentalCount 
    FROM rental 

    INNER JOIN inventory 
    ON rental.inventory_id = inventory.inventory_id 

    WHERE YEAR(rental.rental_date) = 2005 

    GROUP BY MONTH(rental.rental_date), inventory.store_id 
    ) c 
ON b.maxRentals = c.rentalCount 

GROUP BY b.month; 

注意如何與子查詢「c」的別名與別名「a」完全相同。我不確定是否有辦法擺脫這種情況，因爲我不能在別名上加入內聯。我只是堅持一個巨大的查詢，還是有什麼我可以做的？

Answer 1

我90％肯定這個查詢將實現你的意圖：

SELECT MONTH(r.rental_date), i.store_id, COUNT(*) 
FROM rental r 
LEFT JOIN inventory i ON r.inventory_id = i.inventory_id 
WHERE YEAR(r.rental_date) = 2005 
GROUP BY MONTH(r.rental_date), i.store_id 

讓我知道如何去！

編輯：回答其存儲位置在2005已經租出去了更多的DVD每個月的問題：

SELECT x.rental_month, x.store_id, MAX(x.rental_count) FROM (
SELECT MONTH(r.rental_date) AS rental_month, i.store_id AS store_id, COUNT(*) AS rental_count 
FROM rental r LEFT JOIN inventory i ON r.inventory_id = i.inventory_id 
WHERE YEAR(r.rental_date) = 2005 
GROUP BY MONTH(r.rental_date), i.store_id) x 
GROUP BY x.rental_month, x.store_id 

我是通過使用別名到處明確，你很可能省略一些。希望這有助於...

編輯：骯髒的黑客：

SELECT x.rental_month, x.store_id, MAX(x.rental_count) FROM (
SELECT MONTH(r.rental_date) AS rental_month, i.store_id AS store_id, COUNT(*) AS rental_count 
FROM rental r LEFT JOIN inventory i ON r.inventory_id = i.inventory_id 
WHERE YEAR(r.rental_date) = 2005 
GROUP BY MONTH(r.rental_date), i.store_id 
ORDER BY MONTH(r.rental_date) ASC, COUNT(*) DESC) x 
GROUP BY x.rental_month 

編號： http://kristiannielsen.livejournal.com/6745.html

但後來這是否滿足你，看到你已經有一個工作查詢.. 。