Mybatis出现Mapped Statements collection already contains value for 

错误原因：

1.mapper中存在id重复的值

2.mapper中的parameterType或resultType为空。

例如：<update id="deleteSchool" parameterType=" "> </update>

Caused by: org.apache.ibatis.builder.BuilderException: Error parsing Mapper XML. Cause: java.lang.IllegalArgumentException: Mapped Statements collection already contains value for com.dmsdbj.itoo.teachingManagement.dao.CourseDao.queryTeacherCourse
at org.apache.ibatis.builder.xml.XMLMapperBuilder.configurationElement(XMLMapperBuilder.java:120)
at org.apache.ibatis.builder.xml.XMLMapperBuilder.parse(XMLMapperBuilder.java:92)
at org.mybatis.spring.SqlSessionFactoryBean.buildSqlSessionFactory(SqlSessionFactoryBean.java:521)
... 83 more
Caused by: java.lang.IllegalArgumentException: Mapped Statements collection already contains value for com.dmsdbj.itoo.teachingManagement.dao.CourseDao.queryTeacherCourse
at org.apache.ibatis.session.Configuration$StrictMap.put(Configuration.java:872)
at org.apache.ibatis.session.Configuration$StrictMap.put(Configuration.java:844)
at org.apache.ibatis.session.Configuration.addMappedStatement(Configuration.java:668)
at org.apache.ibatis.builder.MapperBuilderAssistant.addMappedStatement(MapperBuilderAssistant.java:302)
at org.apache.ibatis.builder.xml.XMLStatementBuilder.parseStatementNode(XMLStatementBuilder.java:109)
at org.apache.ibatis.builder.xml.XMLMapperBuilder.buildStatementFromContext(XMLMapperBuilder.java:135)
at org.apache.ibatis.builder.xml.XMLMapperBuilder.buildStatementFromContext(XMLMapperBuilder.java:128)
at org.apache.ibatis.builder.xml.XMLMapperBuilder.configurationElement(XMLMapperBuilder.java:118)
... 85 more