如何優化此查詢？需要3分鐘才能運行

Question

我有一個包含3個表的數據庫。

1. 具有一排2000-01-01和2040-01-01之間的每個日期共計14610行
2. 甲locations表，其具有用於每一個位置總共12個行
3. 具有一個A receipts表中id和name甲calendar表id和datetime，以及其他幾個不相關的總共約250,000行的字段

如果沒有收據，我試圖根據位置分組的日期範圍內每天獲得receipts的計數。

我有一個工作查詢，但它需要〜3分鐘運行：

SELECT 
    `locations`.`name` AS `location`, 
    `calendar`.`date` AS `date`, 
    COUNT(`receipts`.`id`) AS `count` 
FROM `locations` 
    CROSS JOIN `calendar` 
    LEFT JOIN `receipts` ON `calendar`.`date` = DATE(`receipts`.`datetime`) 
     AND `locations`.`id` = UPPER(LEFT(`receipts`.`id`, 1)) # there is no `location_id` FK. First char of receipts id is same as location id 
WHERE `calendar`.`date` >= '2017-04-01' AND `calendar`.`date` <= '2017-04-07' 
GROUP BY `locations`.`id`, `calendar`.`id` 
ORDER BY `locations`.`name` ASC, `calendar`.`date` ASC; 

我相信它有事情做與WHERE聲明。

我改變了WHERE這個，而不是它運行瞬間，但它不再讓我零計數無收款：

SELECT 
    `locations`.`name` AS `location`, 
    `calendar`.`date` AS `date`, 
    COUNT(`receipts`.`id`) AS `count` 
FROM `locations` 
    CROSS JOIN `calendar` 
    LEFT JOIN `receipts` ON `calendar`.`date` = DATE(`receipts`.`datetime`) 
     AND `locations`.`id` = UPPER(LEFT(`receipts`.`id`, 1)) # there is no `location_id` FK. First char of receipts id is same as location id 
WHERE DATE(`receipts`.`datetime`) >= '2017-04-01' AND DATE(`receipts`.`datetime`) <= '2017-04-07' 
GROUP BY `locations`.`id`, `calendar`.`id` 
ORDER BY `locations`.`name` ASC, `calendar`.`date` ASC; 

然後我開始與子查詢亂搞，但沒有成功：

SELECT 
    `locations`.`name` AS `location`, 
    `cal`.`date` AS `date`, 
    COUNT(`receipts`.`id`) AS `count` 
FROM `locations` 
    CROSS JOIN (
     SELECT `calendar`.`id`, `calendar`.`date` 
     FROM `calendar` 
     WHERE `calendar`.`date` >= '2017-04-01' AND `calendar`.`date` <= '2017-04-07' 
    ) `cal` 
    LEFT JOIN `receipts` ON `cal`.`date` = DATE(`receipts`.`datetime`) 
     AND `locations`.`id` = UPPER(LEFT(`receipts`.`id`, 1)) # there is no `location_id` FK. First char of receipts id is same as location id 
WHERE DATE(`receipts`.`datetime`) >= '2017-04-01' AND DATE(`receipts`.`datetime`) <= '2017-04-07' 
GROUP BY `locations`.`id`, `cal`.`id` 
ORDER BY `locations`.`name` ASC, `cal`.`date` ASC; 

無論如何，我可以加快第一個查詢，因爲這是給我我想要的輸出的那個？

Answer 1

試試這個：

SELECT l.name location, c.date, COUNT(r.id) count 
FROM calendar c 
    left join calendar n on n.Date = c.Date + 1 -- one day after c.date 
    left join (locations l join receipts r 
       on r.id like '%' + l.Id) 
    on r.datetime between c.Date and n.Date 
where c.Date between '2017-04-01' and '2017-04-07' 
GROUP BY l.id, c.id 
ORDER BY l.name, c.date; 

你的問題的原因是：
1.You使用交叉聯接是不必要。交叉連接創建笛卡爾產品（一邊的每一行都與另一邊的每一行相結合）。因此，將字母與十位數字交叉連接將產生260行{A0，A1，A2 ... A9，B1， B2，.... B9 ...等}
2。在你的SQL查詢中有多個（儘管一個就足夠了）的事實會造成查詢處理器不得不從磁盤讀取表的每一行，從而有效地防止它使用可能在表上的任何索引。在過濾器（where子句）或排序（Order by子句）的表中的某列值的函數上使用此功能會執行此操作，因爲查詢處理器無法在不執行該函數的情況下知道函數值是什麼，並且它必須讀取從磁盤上的主表獲取行以獲取執行該函數的基礎值。如果它僅僅是原始列值，並且該列在索引中，那麼處理器不需要讀取主數據表，它可以僅遍歷索引，索引通常是相當小的尺寸並且需要更小的數目的磁盤IO。

這被稱爲SARGable。

如果c.Date + 1是不可能在MySQL，那麼試試這個：

SELECT l.name location, c.date, COUNT(r.id) count 
FROM calendar c 
    left join calendar n on n.Date = 
     (Select min(date) from Calendar -- subquery gets the next day in calendar 
     Where date > c.Date)   
    left join (locations l join receipts r 
       on r.id like '%' + l.Id) 
    on r.datetime between c.Date and n.Date 
where c.Date between '2017-04-01' and '2017-04-07' 
GROUP BY l.id, c.id 
ORDER BY l.name, c.date; 

Answer 2

SELECT 
    `locations`.`name` AS `location`, 
    `calendar`.`date` AS `date`, 
    COUNT(`receipts`.`id`) AS `count` 
FROM `locations` 
    CROSS JOIN `calendar` 
    LEFT JOIN `receipts` ON `calendar`.`date` = DATE(`receipts`.`datetime`) 
     AND `locations`.`id` = UPPER(LEFT(`receipts`.`id`, 1)) # there is no `location_id` FK. First char of receipts id is same as location id 
WHERE `calendar`.`date` BETWEEN '2017-04-01' AND '2017-04-07' 
GROUP BY `locations`.`id`, `calendar`.`id` 
ORDER BY `locations`.`name` ASC, `calendar`.`date` ASC; 

試試上面的查詢。

在這裏，我用BETWEEN而不是<和>。

你也可以在calendar.date這個字段上創建索引。

您可以在子表上添加FOREIGN KEY約束，並在該列上進行連接。在這種情況下，INDEX也會有所幫助。

Answer 3

對不起，我浪費了每個人的時間，但我設法自己解決這個問題。

這裏是我想出查詢它運行瞬間：

SELECT 
    `l`.`name` AS `location`, 
    `c`.`date` AS `date`, 
    COUNT(`r`.`id`) AS `count` 
FROM `locations` AS `l` 
    CROSS JOIN (
     SELECT `calendar`.`id`, `calendar`.`date` 
     FROM `calendar` 
     WHERE `calendar`.`date` >= '2017-04-01' AND `calendar`.`date` <= '2017-04-07' 
    ) `c` 
    LEFT JOIN (
     SELECT `receipts`.`id`, `receipts`.`datetime` 
     FROM `receipts` 
     WHERE DATE(`receipts`.`datetime`) >= '2017-04-01' AND DATE(`receipts`.`datetime`) <= '2017-04-07' 
    ) `r` ON `c`.`date` = DATE(`r`.`datetime`) AND `l`.`id` = UPPER(LEFT(`r`.`id`, 1)) 
GROUP BY `l`.`id`, `c`.`id` 
ORDER BY `l`.`name` ASC, `c`.`date` ASC;