sql - SQL Server 中的表变量和空值检查

Question

我有以下查询。

CREATE TYPE [dbo].[DeptIdList] AS TABLE(
    [DepartmentId] [smallint] NULL
)
GO
set nocount on

declare @department_ids DeptIdList
declare @tableContainsRecords int = 0

insert into @department_ids
values
(5), (6), (7), (8), (9)

select d.DepartmentID, d.Name, d.GroupName
  from HumanResources.Department as d
  right outer join @department_ids as di on
    d.DepartmentID = di.DepartmentID

@department_ids如果包含行，我想选择特定部门；如果不是，SELECT则应返回部门表中的所有记录。

最简单和最佳的方法是什么？

Answer 1

这应该有效：

SELECT d.DepartmentID, d.Name, d.GroupName
FROM HumanResources.Department d
WHERE DepartmentID IN (SELECT DepartmentID FROM @department_ids)
OR (SELECT COUNT(*) FROM @department_ids) = 0