绝对初学者，尝试在 MySQL 中限制和订购 DELETE/JOIN 查询

Question

我收到了一个 MySQL 查询，用于删除数百万个我试图添加 LIMIT 的整体，这也是 ASC 的 ORDERS。我不知道自己在做什么，而且我很困惑。

据我了解，您无法限制多表 DELETE，但我发现绕过此问题的解决方案过于复杂，我无法自行调整。

DELETE a,b,c
FROM wp_posts a
LEFT JOIN wp_term_relationships b ON ( a.ID = b.object_id )
LEFT JOIN wp_postmeta c ON ( a.ID = c.post_id )
LEFT JOIN wp_term_taxonomy d ON ( d.term_taxonomy_id = b.term_taxonomy_id )
LEFT JOIN wp_terms e ON ( e.term_id = d.term_id )
WHERE d.taxonomy = 'edd_log_type' AND a.post_type = 'edd_log' AND e.term_id = 167
ORDER BY ID ASC LIMIT 100;

期望：我正在尝试构建一个查询，该查询将查找并删除最旧的 100 个条目。我设置了一个 LIMIT，因为正在处理的条目数量（数百万）会超时查询。

实际结果：据我所知，由于 LIMIT 不适用于多表删除导致的语法错误。

Answer 1

您不应该在 where 子句中使用与左连接表相关的列，因为将 where 用作内连接 在这些情况下，您应该在 ON 子句中移动相关条件

对于删除（基于您的代码），您可以将您的 delete statemente 加入到返回您需要的 100 id 的查询中

  delete a,b,c 
  FROM wp_posts a
  LEFT JOIN wp_term_relationships b ON ( a.ID = b.object_id )
  LEFT JOIN wp_postmeta c ON ( a.ID = c.post_id )
  LEFT JOIN wp_term_taxonomy d ON ( d.term_taxonomy_id = b.term_taxonomy_id ) AND d.taxonomy = 'edd_log_type'
  LEFT JOIN wp_terms e ON ( e.term_id = d.term_id ) AND e.term_id = 167
  INNER JOIN  ( 

      select a.id 
      FROM wp_posts a
      LEFT JOIN wp_term_relationships b ON ( a.ID = b.object_id )
      LEFT JOIN wp_postmeta c ON ( a.ID = c.post_id )
      LEFT JOIN wp_term_taxonomy d ON ( d.term_taxonomy_id = b.term_taxonomy_id ) AND d.taxonomy = 'edd_log_type'
      LEFT JOIN wp_terms e ON ( e.term_id = d.term_id ) AND e.term_id = 167
      WHERE a.post_type = 'edd_log'
      ORDER BY ID ASC 
      LIMIT 100

  ) t ON t.id = a.id 
  WHERE AND a.post_type = 'edd_log'

正如草莓所建议的那样，删除更好的是使用内连接（你不能删除不匹配的行）

  delete a,b,c 
  FROM wp_posts a
  INNER  JOIN wp_term_relationships b ON ( a.ID = b.object_id )
  INNER  JOIN wp_postmeta c ON ( a.ID = c.post_id )
  INNER  JOIN wp_term_taxonomy d ON ( d.term_taxonomy_id = b.term_taxonomy_id ) AND d.taxonomy = 'edd_log_type'
  INNER  JOIN wp_terms e ON ( e.term_id = d.term_id ) AND e.term_id = 167
  INNER JOIN  ( 

      select a.id 
      FROM wp_posts a
      INNER  JOIN wp_term_relationships b ON ( a.ID = b.object_id )
      INNER  JOIN wp_postmeta c ON ( a.ID = c.post_id )
      INNER  JOIN wp_term_taxonomy d ON ( d.term_taxonomy_id = b.term_taxonomy_id ) AND d.taxonomy = 'edd_log_type'
      INNER  JOIN wp_terms e ON ( e.term_id = d.term_id ) AND e.term_id = 167
      WHERE a.post_type = 'edd_log'
      ORDER BY ID ASC 
      LIMIT 100

  ) t ON t.id = a.id 
  WHERE AND a.post_type = 'edd_log'