如何使用Nhibernate從連接兩個具有所有ID的表的表中選擇只有一個不同的列的多個列，

Question

以下是我的表結構：

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
    )

我的問題是，當我選擇多個列並在所有主鍵和外鍵都為UNIQUEIDENTIFIER一列上應用DISTINCT ，該時間查詢會給出錯誤消息。 我的查詢和錯誤如下：

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

錯誤消息是：

消息8117，級別16，狀態1，行2操作數數據類型uniqueidentifier對min運算符無效。

但是，如果主鍵和外鍵為int，則上述查詢將成功執行，因為min函數支持整數，但是如何使用uniqueidentifier鍵選擇不同的記錄。

以下是我的Nhibernate查詢：-

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>();

如何按照上述sql查詢先在sql中執行不同的查詢？

Answer 1

只需將UniqueIdentifier轉換為字符串

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