Question

这两个mysql查询返回相同的结果集。要么给我我想要的结果。但是一个优于另一个吗？

SELECT links.*, users.user_name 
FROM links 
LEFT JOIN terms 
ON links.link_id = terms.terms_link_id 
LEFT JOIN users 
ON links.link_user = users.user_id 
WHERE terms.terms_tag_id = ?

-

SELECT links.*, users.user_name 
FROM links, users, terms 
WHERE links.link_id = terms.terms_link_id 
AND links.link_user = users.user_id 
AND terms.terms_tag_id = ?

Answer 1

看起来这回答了你的问题： Inner join vs Where

Answer 2

两者都糟糕

SELECT links.*, users.user_name
FROM links 
INNER JOIN terms 
  ON links.link_id = terms.terms_link_id AND terms.terms_tag_id = $tag_id
INNER JOIN users 
  ON links.link_user = users.user_id;

只有一条规则

执行执行计划，DESC EXTENDED YOUR_QUERY;以检查如何在mysql上进行优化

两个mysql查询，结果相同：一个比另一个好吗？

2 个答案: