如何使用 Nhibernate 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 UNIQUEIDENTIFIER

Posted 2023-04-12

【中文标题】如何使用 Nhibernate 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 UNIQUEIDENTIFIER

【英文标题】：how to select multiple columns with only one distinct column from joining two tables with all id's are UNIQUEIDENTIFIER using Nhibernate

【发布时间】：2017-12-08 18:19:02

【问题描述】：

以下是我的表结构：

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所有主键和外键为 UNIQUEIDENTIFIER 的列上应用 DISTINCT 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：

消息 8117，级别 16，状态 1，行 2 操作数数据类型唯一标识符对 min 运算符无效。

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 min 函数支持整数但是我如何使用 uniqueidentifier 键选择不同的记录。

以下是我的 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？

【参考方案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