mysql like 问题求教

在看 discuz 时候，发现搜索帖子时候

1 个关键词
SELECT t.tid, t.closed, t.author, t.authorid FROM pre_forum_thread t WHERE t.fid IN ('2','36','37','4','39') AND t.displayorder>='0' AND (0 OR t.subject LIKE '%key%') ORDER BY tid DESC LIMIT 500

多个关键词：

SELECT t.tid, t.closed, t.author, t.authorid FROM pre_forum_thread t WHERE t.fid IN ('2','36','37','4','39') AND t.displayorder>='0' AND (1 AND t.subject LIKE '%key%' AND t.subject LIKE '%key1%') ORDER BY tid DESC LIMIT 500

就是 0 OR 与 1 AND 链接 like，这个有什么用处吗？
是防止 SQL 注入吗？