为了从 Sql 查询中以随机顺序获取结果,我通常按新的 Guid 进行排序。我之前已经使用实体框架完成了此操作,但由于某种原因它现在不起作用。
例如(使用 Adventureworks2008r2 数据库)我在 LinqPad 中运行以下查询:
(from t in Employees
orderby Guid.NewGuid()
select new {t.Person.FirstName,t.Person.LastName,t.JobTitle})
这会生成以下 SQL:
SELECT [t1].[FirstName], [t1].[LastName], [t0].[JobTitle]
FROM [HumanResources].[Employee] AS [t0]
INNER JOIN [Person].[Person] AS [t1] ON
[t1].[BusinessEntityID] = [t0].[BusinessEntityID]
那么我的 orderby 查询发生了什么?
我通过以下查询更进一步发现Guid.NewGuid()
仅被调用一次。
(from r in (from t in Employees
select new {t.Person.FirstName,t.Person.LastName,t.JobTitle,
g = Guid.NewGuid()})
orderby r.g
select r)
这生成了以下 SQL 查询
-- Region Parameters
DECLARE @p0 UniqueIdentifier = '68ad5016-19ca-4e31-85c3-1d45618ea8c9'
-- EndRegion
SELECT [t2].[FirstName], [t2].[LastName], [t2].[JobTitle]
FROM (
SELECT [t1].[FirstName], [t1].[LastName], [t0].[JobTitle], @p0 AS [value]
FROM [HumanResources].[Employee] AS [t0]
INNER JOIN [Person].[Person] AS [t1] ON
[t1].[BusinessEntityID] = [t0].[BusinessEntityID]
) AS [t2]
ORDER BY [t2].[value]
知道发生了什么事吗?