I can not believe the same SQL Mybatis database query results and did not do the same!

I. Description of the problem

mybatis query no results, run the same sql database query results, as follows

• This is a database record

  
  

  

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• This is mybatis check out the results, the number of records 0

  
  

  

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• This is exactly the same as the console directly to the sql query into Navicat execution result, a number of records

  
  

  

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Second, the solution

The wherefollowing conditions username = '${username}'and and password = '${password}'set to the same line

    <select id="selectByUsernameAndPassword" resultMap="BaseResultMap" parameterType="string">
        SELECT
        <include refid="Base_Column_List" />
        FROM user
        where username = '${username}'
        and password = '${password}'
    </select>

    <select id="selectByUsernameAndPassword" resultMap="BaseResultMap" parameterType="string">
        SELECT
        <include refid="Base_Column_List" />
        FROM user
        where username = '${username}' and password = '${password}'
    </select>

可以看到, 查询结果一致

image.png

三、异常分析

1. 很多小伙伴都遇到过类似问题, 很懵逼, 难不成mybatis bug? 没, 原因可能千万种, 但根本原因基本上就一个, 那就是实际查询语句与我们看到的sql不一致, 即, sql写的有问题

2. 再来分析一下上面这个问题, 看似xml sql没有问题, 控制台打印的sql也没问题, 但放到数据库执行结果就不一致了, 因为, xml sql两个条件换行了, mybatis实际执行的sql是这样的:

SELECT id, username, password FROM user where username = 'aaa' # '' and password = 'xxx'

并不是控制台打印的sql:

SELECT id, username, password FROM user where username = 'aaa' # '' and password = 'xxx'

查询结果自然不一致

四、总结

本文只是提供一种解决类似问题的思路, 出错原因可能不一样, 但问题关键就是实际执行的sql不一致, 才会导致mybatis和mysql查询结果不一致, 所以, 仔细点, 检查sql

Also, this paper is to test sql injection, so with the ${username}actual use should be#{}