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lixuda
V2EX    MySQL

mysql like 问题求教

  •  
  •   lixuda 2021-01-13 10:24:33 +08:00 2547 次点击
    这是一个创建于 1730 天前的主题,其中的信息可能已经有所发展或是发生改变。
    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?
    4 条回复    2021-01-13 15:56:43 +08:00
    eason1874
        1
    eason1874  
       2021-01-13 10:34:32 +08:00
    不是安全考虑,就是为了方便,没查询价值的,查询的时候会被优化掉。

    其中一个条件为真,那就整个前缀 where 0,后面所有追加直接 OR condition 就行了,不用判断是不是第一个,要不要写 OR

    所有条件为真就整个前缀 where 1,后面追加直接 AND condition
    taogen
        2
    taogen  
       2021-01-13 10:37:38 +08:00 via Android
    可能是方便动态拼接 SQL
    msg7086
        3
    msg7086  
       2021-01-13 15:46:45 +08:00   2
    当年还没有各种 ORM,所以要复杂的检索查询就需要手拼查询字符串。
    就像上面说的,先放一个 "1",然后后面每次追加 "AND xxx LIKE xxx",比合并条件然后再去删掉一个 AND 方便。
    sodadev
        4
    sodadev  
       2021-01-13 15:56:43 +08:00 via Android
    主要是懒
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