使用LEFT OUTER JOIN和WHERE的MySQL查詢

Question

我有三個表： stories ， story_types和comments

以下查詢檢索stories表中的所有記錄，獲取它們的story_types以及與每個故事相關的評論數：

         SELECT s.id AS id,
                s.story_date AS datetime,
                s.story_content AS content,
                t.story_type_label AS type_label,
                t.story_type_slug AS type_slug,
                COUNT(c.id) AS comment_count
           FROM stories AS s
LEFT OUTER JOIN story_types AS t ON s.story_type_id = t.id
LEFT OUTER JOIN comments AS c ON s.id = c.story_id 
       GROUP BY s.id;

現在，我只想從stories WHERE s.id = 1 （這是主鍵）中檢索記錄。 我已經嘗試了以下方法，但是它仍然返回所有記錄：

         SELECT s.id AS id,
                s.story_date AS datetime,
                s.story_content AS content,
                t.story_type_label AS type_label,
                t.story_type_slug AS type_slug,
                COUNT(c.id) AS comment_count
           FROM stories AS s
LEFT OUTER JOIN story_types AS t ON s.story_type_id = t.id
                AND s.id = 1
LEFT OUTER JOIN comments AS c ON s.id = c.story_id 
       GROUP BY s.id;

我還在末尾嘗試了WHERE子句，這將引發錯誤。

在這種情況下，有人可以指出這種情況的正確語法嗎？

我正在使用MySQL 5.1.47。 謝謝。

Answer 1

我猜您將WHERE放在GROUP BY之后，這是非法的。 請參閱有關MySQL中SELECT語法的參考 。 嘗試這個：

SELECT
    s.id AS id,
    s.story_date AS datetime,
    s.story_content AS content,
    t.story_type_label AS type_label,
    t.story_type_slug AS type_slug,
    COUNT(c.id) AS comment_count
FROM
    stories AS s
    LEFT JOIN story_types AS t ON s.story_type_id = t.id
    LEFT JOIN comments AS c ON s.id = c.story_id 
WHERE
    s.id = 1
GROUP BY
    s.id;

編者注：我重新格式化了代碼以突出顯示查詢結構

Answer 2

跟進已接受答案的評論：

對我來說，這是不直觀的，第二次加入

這只是概述正確的代碼格式如何增強理解。 這是我通常格式化SQL的方式：

SELECT 
  s.id               AS id,
  s.story_date       AS datetime,
  s.story_content    AS content,
  t.story_type_label AS type_label,
  t.story_type_slug  AS type_slug,
  COUNT(c.id)        AS comment_count
FROM 
  stories                  AS s
  LEFT JOIN story_types    AS t ON t.id = s.story_type_id 
  LEFT OUTER JOIN comments AS c ON s.id = c.story_id 
WHERE
  s.id = 1
GROUP BY
  s.id;

WHERE不在第二個聯接上。 SELECT語句中只允許有一個WHERE子句，並且它始終是頂層的。

PS：還請注意，在許多數據庫引擎（除MySQL外）中，使用GROUP BY子句然后選擇列而不通過諸如MIN() ， MAX()或COUNT()類對列進行聚合是非法的。 恕我直言，這是不好的作風，也是壞習慣。