我下面的查询非常慢，请告诉我原因是什么

问题描述

||

SELECT cm.course_id,xu.full_path,xu.file_name,xu.file_id,xu.virtual_server
FROM cms_doc.xyf_urls xu
LEFT JOIN bb_bb60.course_main cm ON xu.full_path LIKE \'/courses/\' ||
cm.course_id OR xu.full_path LIKE \'/courses/\' || cm.course_id || \'%\'
WHERE xu.full_path NOT LIKE \'/orgs%\'
AND xu.full_path NOT LIKE \'/institution%\'
AND xu.full_path NOT LIKE \'/library%\'
AND xu.full_path NOT LIKE \'/internal%\'
AND xu.full_path NOT LIKE \'/user%\'
ORDER BY cm.course_id 

    

解决方法

之所以缓慢，是因为所有ѭ1都存在，特别是作为

JOIN

的一部分。     ,首先，确保在

xu.full_path

上有一个索引。 其次，两个“ 4”条件之一似乎是多余的。尝试使用此：

SELECT cm.course_id,xu.full_path,xu.file_name,xu.file_id,xu.virtual_server
FROM cms_doc.xyf_urls xu
  LEFT JOIN bb_bb60.course_main cm
    ON xu.full_path LIKE \'/courses/\' || cm.course_id || \'%\'
WHERE xu.full_path NOT LIKE \'/orgs%\'
  AND xu.full_path NOT LIKE \'/institution%\'
  AND xu.full_path NOT LIKE \'/library%\'
  AND xu.full_path NOT LIKE \'/internal%\'
  AND xu.full_path NOT LIKE \'/user%\'
ORDER BY cm.course_id