2.resultMap is also a value type to be returned (generally an object, refer to the example). It can be found from the naming that it is a map object. If you want to use it, you must define it first.

& ltresultmap id = "xxxxx" class = "POJO (such as com.test.a)" >

& lt result column = "id" property = "id" JDBC type = "decimal"/>

& lt result column = "name" property = "name" JDBC type = "varchar"/>

& lt/result map & gt；

Note: The fields appearing in the previous column should appear in the sql statement, and the corresponding class attributes of these fields must be consistent.

This method is adopted because the results of many linked table queries are not necessarily one or an existing pojo, so it is necessary to redefine one to receive it.

3. A pojo corresponding to a table, field or number can be a list set of POJOs corresponding to a table.