本文最后更新于2023.05.06-10:53，某些文章具有时效性，若有错误或已失效，请在下方留言或联系涛哥。
前言
起因是这样，今天在做项目时做了一个多字段的短句LIKE搜索语句。可是不管输入什么字段都能查到，SQL语句如下
SQL
SELECT
AfficheID,
NtcTitle,
NtcContent,
SortCode,
SortName,
IssueTime,
nlogid
FROM
sAffiche
LEFT JOIN tm_sys_notice_log ON AfficheID = affId
AND isDelFlag = 0
AND UserId = '1619'
WHERE
ObjRole LIKE CONCAT ( '%', '920', '%' )
AND concat ( NtcTitle, NtcContent ) LIKE '%dsfdfsdf%'
AND ( SortCode = '21' AND SortName = '紧急' )
OR ( SortCode = '31' AND SortName = '专向' )
ORDER BY
IssueTime DESC
然后后面发现AND 和 OR 的优先级别是AND优先级别要高于OR ，就好比
select * from 字段1=1 or 字段1=2 and 字段2=3
等价于
select * from 字段1=1 or (字段1=2 and 字段2=3 ）
正确写法
select * from （字段1=1 or 字段1=2） and 字段2=3
所以语句应该修改为
SELECT
AfficheID,
NtcTitle,
NtcContent,
SortCode,
SortName,
IssueTime,
nlogid
FROM
sAffiche
LEFT JOIN tm_sys_notice_log ON AfficheID = affId
AND isDelFlag = 0
AND UserId = '1619'
WHERE
ObjRole LIKE CONCAT ( '%', '920', '%' )
AND concat ( NtcTitle, NtcContent ) LIKE '%dsfdfsdf%'
AND ( ( SortCode = '21' AND SortName = '紧急' ) OR ( SortCode = '31' AND SortName = '专向' ) )
ORDER BY
IssueTime DESC
查询正常
