如何使用 Nhibernate select 多列只有一个不同的列来连接两个所有 id 都是 UNIQUEIDENTIFIER 的表

Question

以下是我的table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 select 多个列并在一列上应用 DISTINCT，所有主键和外键都是 UNIQUEIDENTIFIER 时，该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

错误信息是：

Msg 8117, Level 16, State 1, Line 2 Operand data type uniqueidentifier is invalid for min operator.

但是如果主键和外键是 int 那么上面的查询将成功执行，因为最小函数支持整数但是我如何 select 使用 uniqueidentifier 键的不同记录。

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>();

如何按照上面的 sql 查询先在 sql 中执行不同的查询？

Answer 1

只需将 UniqueIdentifier 转换为字符串

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

如何使用 Nhibernate select 多列只有一个不同的列来连接两个所有 id 都是 UNIQUEIDENTIFIER 的表

how to select multiple columns with only one distinct column from joining two tables with all id's are UNIQUEIDENTIFIER using Nhibernate

c#

mysql

sql

nhibernate