请修改一个mysql查询答案

【问题标题】：Modify a mysql query please请修改一个mysql查询
【发布时间】：2018-03-05 22:05:21
【问题描述】：

我有这个问题：

SELECT p.ID
     , p.post_title
     , tr.trid
     , tr.language_code
  FROM ts_posts AS p
  LEFT 
  JOIN ts_icl_translations AS tr 
    ON tr.element_id = p.ID 
   AND tr.language_code IN ('en', 'us')
 WHERE p.post_status='publish' 
    AND p.post_type IN ('teaching-resource', 'post')
 ORDER 
     BY p.post_date DESC;

它返回帖子列表。有些帖子有一个语言版本 - en，其他帖子有例如 2 个语言版本 - en 和 us。

帮助我修改该查询以在条件下返回行：如果 post 有一个 lang 返回一行如果帖子有更多的语言版本返回我们（或者它应该是一个查询参数）

结果应该是这样的：

更新： 我已经修改了查询。它返回的正是我正在寻找的，没有子查询和拥有。

SELECT p.ID
     , p.post_title
     , tr.trid
     , tr.language_code
  FROM ts_posts AS p
 LEFT 
  JOIN ts_icl_translations AS tr 
    ON tr.element_id = p.ID 
   AND tr.language_code IN ('en', 'us')
   LEFT JOIN ts_icl_translations AS tr2
   ON tr.trid = tr2.trid AND tr2.language_code = 'us'

   LEFT JOIN ts_posts AS p2 On p2.ID = tr2.element_id
 WHERE p.post_status='publish' 
    AND p.post_type IN ('teaching-resource', 'post')
    AND tr.language_code = IFNULL(tr2.language_code, 'en')
 ORDER 
     BY p.post_date DESC;

结果

【问题讨论】：

请注意，没有人使用 RIGHT JOIN。它通常被认为比它的左对应物更难掌握
@Strawberry ok，修改为 LEFT JOIN
GL好像有这个，但如果你还在苦苦挣扎，见见Why should I provide an MCVE for what seems to me to be a very simple SQL query
@Strawberry 我找到了解决办法，谢谢
随时发布答案并接受它。这就是这个网站的运作方式。

标签： mysql sql performance query-optimization

【解决方案1】：

如果存在，您想要的是“我们”，否则是任何其他语言。这个怎么样？

select p.ID, p.post_title, tr.trid, tr.language_code
from ts_posts p left join
     (select tr.element_id,
             coalesce( max(case when tr.language_code = 'us' then 'us' end),
                       max(tr.language_code)
                     ) as language_code
      from ts_icl_translations tr
      group by tr.element_id
     ) tre
     on tre.element_id = p.ID left join
     ts_icl_translations tr
     on tr.element_id = p.ID and tr.language_code = tre.language_code
where p.post_status = 'publish' and
      p.post_type in ('teaching-resource', 'post') 
order by post_date desc;

它获得首选语言，首先是“我们”，其次是任何语言。然后它会重新加入翻译以获取更多详细信息。

【讨论】：

嗨，戈登，谢谢您的回复。您的查询返回：screencast.com/t/rf9iQ7fBhd4y
我可能需要使用“有条件”
我使用了这个查询：SELECT p.ID , p.post_title , tr.trid , tr.language_code, count(tr.trid) as lang_count FROM ts_posts AS p RIGHT JOIN ts_icl_translations AS tr ON tr.element_id = p.ID AND tr.language_code IN ('en', 'us') WHERE p.post_status='publish' AND p.post_type IN ('teaching-resource', 'post') GROUP BY trid ORDER BY p.post_date DESC; 它返回了一个几乎我需要的结果。她截图：screencast.com/t/EFbJNkRla6dC
@mrKirill 。 . .不是having，而是group by。

【解决方案2】：

SELECT p.ID
     , p.post_title
     , tr.trid
     , tr.language_code
  FROM ts_posts AS p
 LEFT 
  JOIN ts_icl_translations AS tr 
    ON tr.element_id = p.ID 
   AND tr.language_code IN ('en', 'us')
   LEFT JOIN ts_icl_translations AS tr2
   ON tr.trid = tr2.trid AND tr2.language_code = 'us'

   LEFT JOIN ts_posts AS p2 On p2.ID = tr2.element_id
 WHERE p.post_status='publish' 
    AND p.post_type IN ('teaching-resource', 'post')
    AND tr.language_code = IFNULL(tr2.language_code, 'en')
 ORDER 
     BY p.post_date DESC;

【讨论】：