方法1：只需要查询出name和phone两个字段:使用queryWrapper的select()方法指定要查询的字段

public List selectByWrapper1(){
	QueryWrapper queryWrapper = new QueryWrapper<>();
	queryWrapper.select("username");//指定查询某字段
	List sysUsers=sysUserService.list(queryWrapper);
	return sysUsers;
}

方法2：查询出除age和address外其它所有字段的数据：同样使用queryWrapper的select()方法

 public List selectByWrapper2(){
	 QueryWrapper queryWrapper = new QueryWrapper<>();
	 //查询指定某字段以外的数据
	 queryWrapper.select(
	 	SysUser.class, info ->!info.getColumn().equals("id") && !info.getColumn().equals("email")
	 );
	 List sysUsers=sysUserService.list(queryWrapper);
	 return sysUsers;
 }