Linq-to-SQL Orderby thenby [英] Linq-to-sql orderby thenby

问题描述

我正在使用以下查询语法

I'm using the following query syntax

from table
where 
where
orderby 
orderby

第一个orderby是一个日期，第二个orderby是一个日期.我认为这可以像orderby thenby一样工作，但似乎在做其他事情.

Where the first orderby is a date and second orderby is a date. I would assume this would work like orderby thenby but appears to be doing something else.

1. 如何使用上述语法而不使用扩展语法来进行订购. (明白了)

1. How can I do an orderby thenby using the above syntax without using extension syntax. (Got it)

orderby，orderby有什么作用?

And what does the orderby, orderby do?

推荐答案

然后如何使用上述语法而不使用扩展语法来进行订购.

How can I do an orderby thenby using the above syntax without using extension syntax.

在字段之间使用逗号:

orderby a, b

---

orderby，orderby有什么作用?

And what does the orderby, orderby do?

当您连续两次使用orderby时，概念上将首先使用第一个orderby对元素进行排序，然后使用第二个orderby再次对元素进行排序.因为排序定义为稳定排序(与第二个对象相关联的对象orderby将保持与第一个orderby排序后的顺序相同，这实际上意味着:

When you use orderby twice in a row the elements conceptually will first be sorted using the first orderby, and then sorted again using the second orderby. Because the sorting is defined to be a stable sort (objects which are tied with the second orderby will remain in the same order as after sorting with the first orderby it effectively means that this:

var query = from x in l
            orderby x.A
            orderby x.B
            select x;

等效于:

var query = from x in l
            orderby x.B, x.A
            select x;

结果是将orderby术语与您可能的意图互换了.

The result is that the orderby terms are swapped from what you probably intended.

使用LINQ to SQL进行测试

这可以通过在LINQ to SQL中进行尝试来验证.我创建了以下查询:

This can be verified by trying it in LINQ to SQL. I created the following query:

var query = from a in dc.Orders
            orderby a.Date
            orderby a.CustomerID
            select a;

这是生成的SQL:

SELECT [t0].[ID], [t0].[CustomerID], [t0].[Date], [t0].[Description]
FROM [dbo].[Order] AS [t0]
ORDER BY [t0].[CustomerID], [t0].[Date]

请注意，不会忽略orderby a.Date.这两个术语都包含在ORDER BY子句中，但顺序与您预期的相反.

Note that the orderby a.Date is not ignored. Both terms are included in the ORDER BY clause, but in the opposite order than you might have intended.

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