C# 如何从连接两个具有所有id的表中选择只有一个不同列的多个列'；是使用Nhibernate的唯一标识符

以下是我的表格结构：

create table Department(
    deptid [UNIQUEIDENTIFIER] ROWGUIDCOL DEFAULT NEWSEQUENTIALID() NOT NULL CONSTRAINT Department_P_KEY PRIMARY KEY,
    departmentname varchar(100)
    )

create table Employee(
    empid [UNIQUEIDENTIFIER] ROWGUIDCOL DEFAULT NEWSEQUENTIALID() NOT NULL CONSTRAINT Employee_P_KEY PRIMARY KEY,
    name varchar(50), 
    city varchar(50),     
    deptid UNIQUEIDENTIFIER NOT NULL,
    foreign key(deptid) references Department(deptid) ON DELETE CASCADE ON UPDATE CASCADE
    )

我的问题是，当我选择多个列并在一个列上应用

DISTINCT

，并且所有主键和外键都是

UNIQUEIDENTIFIER

时，时间查询会给出错误消息。我的查询和错误如下：

select distinct(Department.deptid),min(Employee.empid) as empid
from Employee
inner join Department on Department.deptid = Employee.deptid
group by Department.deptid

错误消息是：

Msg 8117，16级，状态1，第2行操作数数据类型uniqueidentifier对于min运算符无效。

但若主键和外键是int，那个么上面的查询将成功执行，因为min函数支持整数，但如何使用uniqueidentifier键选择不同的记录

下面是我的Nhibernate查询：-

EmployeeEntity employeeEntity = new EmployeeEntity();
            employeeEntity.DepartmentMaster = new DepartmentEntity();
            ProjectionList projectionList = Projections.ProjectionList();
            projectionList.Add(Projections.Distinct(Projections.Property<EmployeeEntity>(x => x.DepartmentMaster)).WithAlias(() => employeeEntity.DepartmentMaster));
            projectionList.Add(Projections.Property<EmployeeEntity>(x => x.empid).WithAlias(() => employeeEntity.empid));

            IList<EmployeeEntity> query = null;
            query = NHSession.QueryOver<EmployeeEntity>()
            .Select(projectionList)
            .TransformUsing(Transformers.AliasToBean<EmployeeEntity>()).List<EmployeeEntity>();

EmployeeEntity EmployeeEntity=新EmployeeEntity（）；
employeeEntity.DepartmentMaster=新部门实体（）；
ProjectionList ProjectionList=Projections.ProjectionList（）；
Add（Projections.Distinct（Projections.Property（x=>x.DepartmentMaster））.with别名（（）=>employeeEntity.DepartmentMaster））；
Add（Projections.Property（x=>x.empid）.WithAlias（（）=>employeeEntity.empid））；
IList query=null；
query=NHSession.QueryOver（）
.选择（投影列表）
.TransformUsing（Transformers.AliasToBean（））.List（）；

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如何按照上面的sql查询，首先在sql中执行distinct查询？

只需将UniqueIdentifier转换为字符串即可

select distinct(Department.deptid),min(CAST(Employee.empid AS NVARCHAR(36))) as empid
from Employee
inner join Department on Department.deptid = Employee.deptid
group by Department.deptid