Question

首先，我很想进入SQL的事情，现在我正在研究一个类项目我有一些像

这样的表

表格用户

user_id  |  username | name 
   1     |    nihan  |  Nihan Dip
   2     |     dip   |  Meaw ghew
  more   |  more     | more

表朋友

you    | friend_id  
 1     |    2
 1     |    27
 2     |    9
 more  |   more

表格跟踪

user_id   |  follows
  1       |   99
  7       |   34

表格

post_id   |  user_id  | type  |  content  | post_time
  1       |   1       |  text | loren toren | timestamp
  2       |   2       | text  | ipsum       | timestamp

现在我希望得到用户朋友的帖子以及他跟随的人和他的背景他所以我做了这个SQL

SELECT 
    username, name,content, post_time
FROM
    post
        INNER JOIN
    user ON user.user_id = post.user_id
WHERE
    post.user_id IN (SELECT 
            friend_id
        FROM
            friend
        WHERE
            you = 1 

        UNION ALL 

        SELECT 
            follows
        FROM
            follow
        WHERE
            user_id = 1)
        OR post.user_id = 1
ORDER BY post_time DESC
LIMIT 10

这个查询工作得很好。我只是想知道是否还有优化可以完成？那怎么样？请教我：）

Answer 1

而不是使用IN尝试使用JOIN添加添加更多索引。

SELECT  DISTINCT u.name, u.username,
        p.content, p.post_time
FROM    post p
        INNER JOIN user u
            ON u.user_id = p.user_id
        INNER JOIN
        (
            SELECT  friend_id id
            FROM    friend
            WHERE   you = 1 
            UNION ALL 
            SELECT  follows id
            FROM follow
            WHERE user_id = 1
        ) s ON p.user_id = s.ID
ORDER BY post_time DESC
LIMIT 10

如何优化SQL查询更多？

1 个答案: