案例：

SELECT (@num:=@num+1) AS `index`, name, age
FROM sys_user, (SELECT @num:=0) AS a order by age,name;

查询结果：

 datagrip和dbeaver查询结果不一样，使用cmd查询，默认也是无小数点的

但实际返回结果，其实是带点的 

 

    @Data
public class SysUserDTO {
//    private Integer id;
    private String id;
//    private Integer index;
    private String index;
    private String name;
    private Integer age;
}


    @Test
    void queryWithIndex() {
        List<SysUserDTO> userDTOS = userMapper.queryWithIndex();
        log.info("userDTOS:{}",userDTOS);
    }

    <select id="queryWithIndex" resultType="com.bootmaven.vo.SysUserDTO">
        SELECT (@num:=@num+1) AS `index`, name, age,id
        FROM sys_user, (SELECT @num:=0) AS a order by age,name
    </select>

根据返回类型，mybatis查询有两种不同结果：

userDTOS:[
SysUserDTO(id=1, index=1, name=Jone, age=18), 
SysUserDTO(id=2, index=2, name=Jack, age=20), 
SysUserDTO(id=4, index=3, name=Sandy, age=21), 
SysUserDTO(id=5, index=4, name=Billie, age=24), 
SysUserDTO(id=3, index=5, name=Tom, age=28)]

userDTOS:[
SysUserDTO(id=1, index=1.0, name=Jone, age=18), 
SysUserDTO(id=2, index=2.0, name=Jack, age=20), 
SysUserDTO(id=4, index=3.0, name=Sandy, age=21), 
SysUserDTO(id=5, index=4.0, name=Billie, age=24), 
SysUserDTO(id=3, index=5.0, name=Tom, age=28)]

 上面是Integer接收index，下面为String接收index

即：mysql默认返回的下标其实是带小数点的。（多列带点，单列不带）

参考：MySQL给查询加序号