Mybatis报错——Mapped Statements collection already contains value for 。。。

Mybatis报错——Mapped Statements collection already contains value for com.mapper.EmployeeMapperPlus.getEmpByIdDe

异常如下：

org.apache.ibatis.exceptions.PersistenceException:
### Error building SqlSession.
### The error may exist in com/mapper/EmployeeMapperPlus.xml
### The error occurred while processing mapper_resultMap[MyEmp_disc]_discriminator_case[1]
### Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: org.apache.ibatis.builder.BuilderException: Error parsing Mapper XML.
Cause: java.lang.IllegalArgumentException: Mapped Statements collection already contains value for com.mapper.EmployeeMapperPlus.getEmpByIdDe
at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:80)
... 31 more

报错分析：

关键是这两句：

Error parsing Mapper XML

意思是：Mapper.xml映射文件解析错误

Cause: java.lang.IllegalArgumentException: Mapped Statements collection already contains value for com.mapper.EmployeeMapperPlus.getEmpByIdDe

意思是：映射声明集合中已经包含方法
com.mapper.EmployeeMapperPlus.getEmpByIdDe

报错原因：

Mapper映射文件中SQL标签的id属性，是与Mapper接口中的方法一一对应的。

上面错误顾名思义就是SQL标签中有 id 重复的标签。故而报出映射声明集合中已经包含某方法（Mapped Statements collection already contains value for ）

如下代码，第一个标签与第三个标签id相同就会报这个异常。

<mapper namespace="com.mapper.EmployeeMapperPlus">
<select id="getEmpByIdDe" resultMap="MySinpleEmp">
select * from tbl_employee where id = #{id}
</select>

<select id="getEmpByIdStep" resultMap="MyEmpByStep">
select * from tbl_employee where id = #{id}
</select>
<select id="getEmpByIdDe" resultMap="MyEmp_disc">
select * from tbl_employee where id = #{id}
</select>
</mapper>

错误解决：

查找根据报错提示的映射文件名和方法名，查找是否有id属性重复的SQL标签。