MySQL - 左連接和不在

Question

我嘗試避免子查詢，因爲他們通常比正確的連接性能低得多。

這是我目前不工作查詢：

SELECT 
    a.`email_list_id`, a.`category_id`, a.`name` 
FROM 
    `email_lists`AS a 
    LEFT JOIN `email_autoresponders` AS b 
     ON (a.`website_id` = b.`website_id`) 
WHERE 
    a.`website_id` = [...] 
    AND a.`category_id` <> 0 
    AND a.`email_list_id` <> b.`email_list_id` 
GROUP BY 
    a.`email_list_id` 
ORDER BY a.`name` 

此查詢的工作：

SELECT 
    `email_list_id`, `category_id`, `name` 
FROM 
    `email_lists` 
WHERE 
    `website_id` = [...] 
    AND `category_id` <> 0 
    AND `email_list_id` NOT IN ( 
     SELECT 
      `email_list_id` 
     FROM 
      `email_autoresponders` 
     WHERE `website_id` = [...] 
    ) 
GROUP BY 
    `email_list_id` 
ORDER BY 
    `name` 

有什麼辦法用左連接做到這一點？我嘗試了許多不同的選擇。

Answer 1

重新考慮它一下後，這可能工作，我相信：

SELECT 
    a.`email_list_id`, a.`category_id`, a.`name` 
FROM 
    `email_lists`AS a 
    LEFT JOIN `email_autoresponders` AS b 
     ON (a.`website_id` = b.`website_id` and a.`email_list_id` = b.`email_list_id`) 
WHERE 
    a.`website_id` = [...] 
    AND a.`category_id` <> 0 
    AND b.`email_list_id` is NULL 
GROUP BY 
    a.`email_list_id` 
ORDER BY a.`name` 

Answer 2

對於初學者來說，在email_list_id添加不平等檢查連接標準，而不是你的WHERE子句中有它：

LEFT JOIN `email_autoresponders` AS b 
    ON (a.`website_id` = b.`website_id` 
     AND a.`email_list_id` <> b.`email_list_id`) 

雖然我不知道的情況你提到的廣闊優化通話，這是使用聯接，而不是子查詢的方式...