Question

我有2个mysql查询，检索相同的数据？，您认为哪个更好用，为什么？考虑到标准，更好的代码等对不起，如果这是一个愚蠢的问题，但我是一个好奇的猫！所以这里：

QUERY 1：

SELECT *
FROM
((
  SELECT u.username, u.picture, m.id, m.user_note, m.reply_id, m.reply_name, m.dt
  FROM   relationships r
  JOIN   notes m ON m.user_id = r.leader
  JOIN   user u ON r.leader = u.user_id
  WHERE  r.listener ='2'
)
UNION ALL
(
  SELECT u.username, u.picture, m.id, m.user_note, m.reply_id, m.reply_name, m.dt
  FROM   notes m
  JOIN   user u ON m.user_id = u.user_id
  WHERE  u.user_id ='2'
)) d
WHERE    d.dt < '2010-09-20_131830'
ORDER BY d.dt DESC

QUERY 2：

SELECT u.username, u.picture, m.id, m.user_note, m.reply_id, m.reply_name, m.dt
FROM notes m
INNER JOIN user u
ON m.user_id = u.user_id
WHERE (m.user_id = '2'
OR m.user_id IN (
   SELECT r.leader
   FROM relationships r
   WHERE r.listener ='2'))
AND dt < '2010-09-20_131830'
ORDER BY dt DESC

Answer 1

我发现UNION ALL版本更容易理解（可能是我的情况）但我会重写如下。

将AND m.dt < '2010-09-20_131830添加到每个部分应该会给您带来更好的表现您可以运行几次并验证它是否有所作为。

SELECT  u.username
        , u.picture
        , m.id
        , m.user_note
        , m.reply_id
        , m.reply_name
        , m.dt 
FROM    relationships r 
        INNER JOIN notes m ON m.user_id = r.leader 
        INNER JOIN user u ON r.leader = u.user_id 
WHERE   r.listener ='2' 
        AND m.dt < '2010-09-20_131830' 
UNION ALL 
SELECT  u.username
        , u.picture
        , m.id
        , m.user_note
        , m.reply_id
        , m.reply_name
        , m.dt 
FROM    notes m 
        INNER JOIN user u ON m.user_id = u.user_id 
WHERE   u.user_id ='2' 
        AND m.dt < '2010-09-20_131830' 
ORDER BY m.dt DESC

什么mysql查询更好？

1 个答案: